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                          PURCHASE AND SALE AGREEMENT

                                    BETWEEN

                        UNION OIL COMPANY OF CALIFORNIA

                                      AND

                                TOM BROWN, INC.

                                     DATED

                                  JUNE 8, 1999




<PAGE>   2





                               TABLE OF CONTENTS
<TABLE>

<S>                                                                           <C>
SECTION 1

         DEFINITIONS...........................................................1
         1.1      Defined Terms................................................1
         1.2      Undefined Financial Accounting Terms.........................9
         1.3      References...................................................9
         1.4      Construction.................................................9

SECTION 2

         PURCHASE AND SALE....................................................10
         2.1      Assets......................................................10
         2.2      Excluded Assets.............................................11
         2.3      Purchase Price..............................................13
         2.4      Payment Procedures..........................................13
         2.5      Adjusted Cash Purchase Price................................13
         2.6      Cash Settlement.............................................13
         2.7      Assumption Agreement........................................14

SECTION 3

         TITLE EXAMINATION....................................................14
         3.1      Access to Title Information.................................14
         3.2      Title Defects...............................................15
         3.3      Notice of Title Defect......................................15
         3.4      Claim Value.................................................15
         3.5      Defect Value................................................15
         3.6      Remedies for Title Defects..................................16
         3.7      Purchase Price Adjustments Threshold........................17
         3.8      Preferential Purchase Rights................................17
         3.9      Preferential Purchase Right Disputes........................18

SECTION 4

         ENVIRONMENTAL MATTERS................................................18
         4.1      No Admission Against Interest...............................18
         4.2      Physical Condition of the Assets............................19
         4.3      Endangered Species, Critical Habitat, Wetlands,
                  Geologic Hazards and Flooding...............................19
</TABLE>


                                       i

<PAGE>   3



<TABLE>

<S>                                                                           <C>
         4.4      Environmental Assessments and Completion of
                  Environmental Due Diligence.................................20
         4.5      Buyer's Access to Assets; Indemnification; Insurance........21
         4.6      Assumption of Environmental Liabilities.....................22
         4.7      Qualified Claim Cost Sharing................................23
         4.8      Limitation..................................................24
         4.9      Termination Due to Material Environmental Deficiencies......24
         4.10     Determination of Value......................................24

SECTION 5

         OPERATIONS AND CASUALTY LOSS.........................................25
         5.1      Operations..................................................25
         5.2      Casualty Loss...............................................26
         5.3      Successor Operator..........................................26
         5.4      Restrictions on Operations..................................26
         5.5      Permit Transfers............................................26

SECTION 6

         REPRESENTATIONS AND WARRANTIES OF UNOCAL.............................27
         6.1      Organization................................................27
         6.2      Authority to do Business....................................28
         6.3      Authority; Enforceability...................................28
         6.4      Litigation, Suits or Claims.................................28
         6.5      Disclaimer of Warranties....................................28
         6.6      Gas Entitlements and Imbalances.............................29
         6.7      No Breach...................................................29
         6.8      Environmental Condition of Assets...........................29
         6.9      Compliance with Laws and Agreements.........................30
         6.10     Taxes.......................................................30
         6.11     No Distribution.............................................30
         6.12     Current Commitments.........................................30
         6.13     Brokers.....................................................30
         6.14     Ownership of Common Stock...................................31
         6.15     Royalties...................................................31

SECTION 7

         REPRESENTATIONS AND WARRANTIES OF BUYER..............................31
         7.1      Organization................................................31
</TABLE>


                                       ii

<PAGE>   4

<TABLE>

<S>                                                                           <C>
         7.2      Authority; Enforceability...................................31
         7.3      Consents....................................................32
         7.4      Litigation, Suits or Claims.................................32
         7.5      No Breach...................................................32
         7.6      Compliance with Laws and Agreements.........................32
         7.7      Investigations of Assets....................................32
         7.8      No Distribution.............................................33
         7.9      Federal Leases..............................................33
         7.10     Capitalization of Buyer; Title to the Shares................33
         7.11     SEC Filings.................................................33
         7.12     Financial Statements........................................34
         7.13     Absence of Certain Changes..................................34
         7.14     Regulatory Authority........................................36
         7.15     Environmental Matters.......................................36
         7.16     Brokers.....................................................36

SECTION 8

         CONDITIONS PRECEDENT TO THE OBLIGATIONS OF UNOCAL....................36
         8.1      Purchase Price..............................................36
         8.2      Buyer's Representations and Warranties True and Correct.....36
         8.3      Officer's Certificate.......................................36
         8.4      Opinion of Counsel..........................................37
         8.5      Pre-Closing Performance.....................................37
         8.6      Authorization...............................................37
         8.7      Absence of Litigation.......................................38
         8.8      Bonds.......................................................38
         8.9      Hart-Scott-Rodino Act.......................................38
         8.10     Stock Ownership and Registration Rights Agreement...........38
         8.11     Certificates of Insurance...................................38
         8.12     Permits, Consents and Preferential Purchase Rights..........38
         8.13     Satisfactory Results of Unocal's Diligence..................38

SECTION 9

         CONDITIONS PRECEDENT TO THE OBLIGATIONS OF BUYER.....................38
         9.1      Delivery of Cash Settlement.................................39
         9.2      Delivery of Instruments of Transfer.........................39
         9.3      Unocal's Representations and Warranties True and Correct....39
         9.4      Officer's Certificate.......................................39
         9.5      Opinion of Counsel..........................................39
</TABLE>


                                      iii

<PAGE>   5


<TABLE>

<S>                                                                           <C>
         9.6      Pre-Closing Performance.....................................40
         9.7      Authorization...............................................40
         9.8      Absence of Litigation.......................................40
         9.9      Hart-Scott Rodino Act.......................................40
         9.10     Stock Ownership and Registration Rights Agreement...........40
         9.11     Consents....................................................40
         9.12     Satisfactory Results of Buyer's Diligence...................40
         9.13     No Material Changes.........................................40

SECTION 10

         COVENANTS............................................................41
         10.1     Investigation and Decision..................................41
         10.2     Access to Information.......................................42
         10.3     Gas Imbalances and Pipeline Imbalances......................43
         10.4     Hart-Scott-Rodino Act.......................................44
         10.5     Third-Party Consents........................................44
         10.6     Completion of Due Diligence.................................45
         10.7     Additional Agreements.......................................45
         10.8     Payment of Certain Expenses Due and Payable After the 
                  Closing Date................................................45
         10.9     Notification of Certain Matters.............................45
         10.10    Announcements...............................................46
         10.11    Termination of Guarantees and Other Commitments.............46
         10.12    Access to Geologic and Geophysical Information..............46
         10.13    Collection of Certain Insurance Proceeds....................47

SECTION 11

         EMPLOYEE MATTERS.....................................................47
         11.1     Offer to Employees..........................................47
         11.2     Recognition of Service Time.................................47
         11.3     Hired Employee List.........................................47
         11.4     Terminated Employees........................................47
         11.5     Employment Restriction......................................47

SECTION 12

         TAXES................................................................48
         12.1     Apportionment of Ad Valorem and Property Taxes..............48
         12.2     Sales Taxes, Filing Fees, Etc...............................48
         12.3     Other Taxes.................................................48
</TABLE>


                                       iv

<PAGE>   6

<TABLE>

<S>                                                                           <C>
SECTION 13

         TERMINATION..........................................................48
         13.1     Termination.................................................49
         13.2     Effect of Termination.......................................49
         13.3     Specific Performance........................................49

SECTION 14

         SURVIVAL AND INDEMNIFICATION.........................................49
         14.1     Survival....................................................49
         14.2     Indemnification.............................................50
         14.3     Third Party Claims..........................................51
         14.4     Method of Asserting Claims..................................51
         14.5     Right to Cure...............................................54
         14.6     Exclusive Remedy............................................54
         14.7     RELEASE, INDEMNITY AND WAIVER...............................54

SECTION 15

         CLOSING..............................................................55
         15.1     Time of Essence.............................................55
         15.2     Place and Date..............................................55
         15.3     Unocal's Actions at Closing.................................55
         15.4     Buyer's Actions at Closing..................................57
         15.5     Closing Statement...........................................57
         15.6     Notices.....................................................57

SECTION 16 ACTIONS AFTER CLOSING..............................................58
         16.1     Final Accounting............................................58
         16.2     Receipts and Credits........................................58
         16.3     Suspended Funds.............................................59
         16.4     Further Assurances..........................................59
         16.5     Recording...................................................59
         16.6     Books and Records...........................................59
         16.7     Post Closing Access to Properties and Records by Unocal.....60

SECTION 17

         MISCELLANEOUS........................................................60
</TABLE>


                                       v

<PAGE>   7


<TABLE>

<S>                                                                           <C>
         17.1     Governing Law...............................................60
         17.2     Assignment..................................................60
         17.3     Written Notices.............................................61
         17.4     Expenses....................................................62
         17.5     Waiver of Compliance with Bulk Transfer Laws................62
         17.6     WAIVER OF CONSUMER RIGHTS...................................62
         17.7     Waiver of Jury Trial........................................63
         17.8     WAIVER OF PUNITIVE AND CONSEQUENTIAL DAMAGES................63
         17.9     No Admissions...............................................63
         17.10    Use of Unocal's Name........................................63
         17.11    Entire Agreement, Etc.......................................63
         17.12    Parties in Interest.........................................64
         17.13    Severability................................................64
         17.14    Consents....................................................64
</TABLE>

                                       vi

<PAGE>   8





                       SCHEDULE OF SCHEDULES AND EXHIBITS
<TABLE>

<S>                  <C>  <C>                               
Schedule 2.1(i)        -   LEASEHOLD INTERESTS
Schedule 2.1(ii)       -   OIL & GAS PROPERTIES
Schedule 2.1(iii)      -   LISBON PLANT
Schedule 2.1(vi)       -   PERSONAL PROPERTY, WAREHOUSE STOCK AND IDLE EQUIPMENT
Schedule 2.1(ix)       -   PIPELINE ASSETS
Schedule 2.1(xii)      -   VEHICLES
Schedule 2.2(ii)       -   EXCLUDED INTERESTS
Schedule 3.8           -   PREFERENTIAL RIGHTS
Schedule 4.7           -   QUALIFIED CLAIM COST SHARING ALLOCATION
Schedule 6.6           -   GAS AND PIPELINE BALANCING SCHEDULE
Schedule 6.8           -   ENVIRONMENTAL DISCLOSURE SCHEDULE
Schedule 6.12          -   CURRENT COMMITMENTS
Schedule 9.11          -   CONSENTS
Schedule 11.1          -   LISBON PLANT-BASED EMPLOYEES
</TABLE>


                                    EXHIBITS

<TABLE>

<S>             <C>       <C>                               
Exhibit "A"       -        CLAIM VALUE FORMULA AND ALLOCATED VALUES SCHEDULE
Exhibit "B"       -        ARBITRATION PROCEDURES
Exhibit "C"       -        ENVIRONMENTAL ASSESSMENTS
Exhibit "D"       -        UNOCAL DISCLOSURE SCHEDULE
Exhibit "E-1"     -        GEOPHYSICAL DATA LICENSING AGREEMENT
Exhibit "E-2"     -        GEOPHYSICAL DATA
Exhibit "F-1"     -        ASSIGNMENT OF LEASES, BILL OF SALE AND ASSIGNMENT OF INTANGIBLE
                           CONTRACTUAL RIGHTS AND OTHER INTANGIBLE PROPERTY
Exhibit "F-2"     -        RIGHT-OF-WAY ASSIGNMENT AND BILL OF SALE
Exhibit "F-3"     -        TERM ROYALTY DEED ROYALTIES
Exhibit "G"       -        ASSUMPTION AGREEMENT
Exhibit "H-1"     -        BUYER'S SATISFACTORY COMPLETION OF DUE DILIGENCE
Exhibit "H-2"     -        UNOCAL'S SATISFACTORY COMPLETION OF DUE DILIGENCE
Exhibit "I"       -        LEASE AGREEMENT
Exhibit "J"       -        STOCK OWNERSHIP AND REGISTRATION RIGHTS AGREEMENT
</TABLE>



                                      vii

<PAGE>   9


                          PURCHASE AND SALE AGREEMENT

         THIS PURCHASE AND SALE AGREEMENT is entered into as of the 8th day of
June, 1999, by and between Union Oil Company of California, a California
corporation, with an office at 14141 Southwest Freeway, Sugar Land, Texas 77478
(hereinafter referred to as "Unocal"), and Tom Brown, Inc., a Delaware
corporation, whose address is 508 West Wall, Suite 500, Midland, Texas 79702
(referred to herein as "Buyer" or "TBI").

                                    RECITALS

         WHEREAS, Unocal and its subsidiary Unocal Pipeline Co. ("Pipeline")
are the holders of certain assets which include certain oil and gas interests
and properties in the states of Colorado, Wyoming, North Dakota and Utah, a gas
processing and treatment plant in San Juan County, Utah and an approximate 66
mile, 10 inch pipeline from such plant to Aneth, Utah; and

         WHEREAS, Unocal desires to sell assets, as hereinafter described, to
Buyer and Buyer desires to purchase such assets from Unocal, upon the terms and
subject to the conditions set forth in this Agreement; and

         WHEREAS, as full consideration for the Assets, TBI (i) will issue to
Unocal 5.8 million shares of fully paid, non-assessable common stock of TBI,
par value of $0.10 per share (the "Common Stock") and (ii) pay Unocal five
million dollars ($5,000,000) in cash subject to adjustments as described
herein;

         NOW, THEREFORE, in consideration of the covenants and agreements
contained herein, Unocal and Buyer agree as follows:

                                   SECTION 1

                                  DEFINITIONS

1.1      DEFINED TERMS: The following terms, when capitalized in this
         Agreement, shall have the meanings defined either in this Section or
         elsewhere in this Agreement.

"ADJUSTED CASH PURCHASE PRICE" shall have the meaning specified in Section 2.5.

"ACCRUING" or "ACCRUED" means, with respect to any obligation, duty, loss,
liability, claim, fine, expense, damage, cost or penalty, the occurring or
happening of any event which causes such obligation, duty, loss, liability,
claim, fine, expense, damage, cost or penalty to become demandable, requirable,
assertible, enforceable, due and owing, or being incurred or occurring, as the
case may be.


                                       1

<PAGE>   10





"AFFILIATE" means, with respect to any specified Person, any other Person
directly or indirectly controlling, controlled by, or under common control
with, such Person. For purposes of this definition, "control" shall mean the
possession, directly or indirectly, of the power to direct or cause the
direction of the management and policies of such Person, whether through the
ownership of voting securities or otherwise.

"AGREEMENT" means this Purchase and Sale Agreement, including all Schedules and
Exhibits.

"ALLOCATED VALUE(S)" means the value of certain of the Assets as set forth in
Exhibit A.

"ASSETS" shall have the meaning specified in Section 2.1.

"ASSUMED LIABILITIES" means all Environmental Liabilities, General Liabilities,
Plugging and Abandonment Obligations and other liabilities expressly assumed by
Buyer under the terms of this Agreement.

"CASH SETTLEMENT" shall have the meaning specified in Section 2.6.

"CASUALTY LOSS" means a loss of personalty, excluding oil, gas and other
minerals in place, that is caused by a sudden, unexpected and unusual event.

"CLAIM NOTICE" means notification by an Indemnified Party to an Indemnifying
Party of any claim or demand for which the Indemnifying Party would be liable
hereunder, and providing information which specifies the nature and basis of
the claim or demand and the amount or the estimated amount of the claim or
demand.

"CLAIM VALUE" shall have the meaning specified in Section 3.4.

"CLAIM VALUE FORMULA" shall have the meaning specified in Exhibit "A," or if
none is provided therein, the claim value formula mutually agreed to by the
parties in writing.

"CLOSING" means the consummation of the transactions contemplated in this
Agreement other than any transactions specifically scheduled for a time after
Closing by the terms hereof.

"CLOSING DATE" means the date specified in Section 15.2, or such other date as
the parties may mutually agree upon in writing.

"CONFIDENTIALITY AGREEMENT" means those Confidentiality Agreements between the
Parties dated June 16, 1998, and any amendments thereto, executed prior to and
in conjunction with and for the purposes of this Agreement.



                                       2

<PAGE>   11





"CONTRACT RIGHTS" means the Assets described in Section 2.1(vii).

"DEFECT VALUE" shall have the meaning specified in Section 3.5.

"DEFENSIBLE TITLE" means title which is determinable of record, and is free of
liens, claims, defects, encumbrances or deficiencies other than Permitted
Encumbrances.

"DELETERIOUS SUBSTANCE" means (i) any substance, product, waste or other
material of any nature whatsoever which is or becomes listed as a hazardous
substance, hazardous waste, hazardous material or pollutant under any
Environmental Laws; (ii) any substance, product, waste or other material of any
nature whatsoever which may give rise to liability under any Environmental
Laws; (iii) petroleum and its fractions, crude oil and other petroleum
products; and (iv) radioactive materials including but not limited to naturally
occurring radioactive materials.

"DUE DILIGENCE PERIOD" means the time period between the date hereof and seven
(7) calendar days prior to the Closing Date.

"EFFECTIVE DATE" means 8:00 a.m. Central Standard Time, on January 1, 1999.

"EMPLOYEE RELATED LIABILITIES" means obligations, duties and liabilities for
claims made by, or relating to, Unocal employees or consultants which Accrued
and are attributable to periods, prior to the Closing Date.

"ENVIRONMENTAL ASSESSMENTS" shall have the meaning specified in Exhibit "C" or
in Section 4.4.

"ENVIRONMENTAL DISCLOSURE SCHEDULE" means Schedule 6.8 to this Agreement.

"ENVIRONMENTAL LAWS" means any applicable laws, orders, rules, regulations,
judgments or decrees of any federal, state, tribal, county or municipal
governing authority having jurisdiction over any Asset or Party which relate to
pollution, the protection or cleanup of the environment, or the release or
disposal of Deleterious Substances into the environment, including but not
limited to ambient air, surface water, groundwater, land surface or subsurface
strata; including all such laws, orders, rules, regulations, judgments or
decrees as they may be amended, varied or modified in the future.

"ENVIRONMENTAL LIABILITIES" means all obligations, duties, losses, liabilities,
claims, fines, expenses, damages, costs (including attorney's fees and
expenses) or penalties created by, related to, or arising out of any
Environmental Law, whether Accruing before or after the Effective Date;
excluding all Plugging and Abandonment Obligations.

"EXCLUDED ASSETS" shall have the meaning specified in Section 2.2.



                                       3

<PAGE>   12





"EXECUTION DATE" means the date on which this Agreement has been fully executed
by Unocal and TBI.

"FACILITIES" shall have the meaning specified in Section 2.1(iv).

"FINAL ACCOUNTING" shall have the meaning specified in Section 16.1.

"GAS IMBALANCE" means the difference between the volume of produced gas that
Unocal took from an Asset(s) and the volume of Unocal's gas entitlement for
such Asset(s).

"GENERAL LIABILITIES" means all obligations, duties, losses, liabilities,
claims, fines, expenses, damages, costs (including attorneys fees and expenses)
or penalties created by, related to, or arising out of ownership or operation
of the Assets, any Contract Rights, or compliance with any applicable law,
order, rule, regulation, judgment or decree of any federal, state, tribal,
county or municipal governing authority having jurisdiction over the Assets or
the Parties, whether Accruing before or after the Effective Date.
Notwithstanding the above, the term "General Liabilities" shall not include:

                    (a) Plugging and Abandonment Obligations (which are
               addressed elsewhere herein);

                    (b) Environmental Liabilities (which are addressed
               elsewhere herein);

                    (c) Pre-Effective Date Royalties and Tax Payments;

                    (d) Employee Related Liabilities;

                    (e) All items of threatened or pending litigation and
               proceedings set forth in Paragraph A of Exhibit D attached
               hereto to the extent attributable to monetary damages relating
               to Pre-Effective Date periods; and

                    (f) General Liabilities (exclusive of items (a) through (e)
               above) which Accrued prior to the Effective Date which are in
               excess of $200,000 in the aggregate and are asserted pursuant to
               written claims made by third parties to Unocal or Buyer within
               five (5) years after the Closing Date.

For purposes of clarification, (i) Buyer acknowledges that Buyer shall have
responsibility for (x) the initial $200,000 in the aggregate of General
Liabilities which Accrued prior to the Effective Date and are asserted within
five (5) years after the Closing Date, (y) any General Liabilities which
Accrued prior to the Effective Date which are not asserted in writing by third
parties against Unocal or Buyer within five (5) years after the Closing Date;
and (z) any General Liabilities which Accrue after the Effective Date and (ii)
Unocal acknowledges that Unocal shall have responsibility for (x)


                                       4

<PAGE>   13





liabilities pertaining to Excluded Assets, (y) liabilities referenced in
subsections (c), (d), (e) and (f) above and (z) liabilities with respect to a
portion of the Qualified Claims to the extent expressly provided in Section 4
hereof.

"GEOPHYSICAL DATA LICENSING AGREEMENT" means the agreement attached hereto and
designated as Exhibit "E-1."

"GEOPHYSICAL SEISMIC LICENSING PRICE" means the initial fee of $1.00, together
with all other fees and charges described in the Geophysical Data Licensing
Agreement, which TBI will pay to Unocal to license the Geophysical Data
described in the Geophysical Data Licensing Agreement.

"GOVERNMENTAL APPROVALS" means consents, approvals, authorizations or orders
required to be obtained from any court or tribunal in any jurisdiction or any
public, or governmental or regulatory body, agency, department, commission,
board, bureau or other authority or instrumentality.

"GOVERNMENTAL LESSOR APPROVALS" means consents, approvals, authorizations or
orders required to be obtained from any court or tribunal in any jurisdiction
or any public, or governmental or regulatory body, agency, department,
commission, board, bureau or other authority or instrumentality which is a
lessor under any of the Leasehold Interests other than consents, approvals,
authorizations or orders of a nature customarily obtained following the closing
of a transaction.

"HART-SCOTT-RODINO ACT" means the Hart-Scott-Rodino Antitrust Improvements Act
of 1976, as amended, and the rules and regulations promulgated thereunder.

"HYDROCARBONS" shall mean all severed crude oil, natural gas, casinghead gas,
drip gasoline, natural gasoline, petroleum, natural gas liquids, plant
products, condensate, and other liquid and gaseous hydrocarbons and minerals of
every kind and description.

"INDEMNIFIED PARTY" and "INDEMNIFYING PARTY" shall have the meaning specified
in Section 14.4.

"KNOWLEDGE" means the actual knowledge of the applicable Party's officers and
salaried employees directly, immediately and materially involved in the
transactions which are the subject matter of this Agreement, and that are equal
to or above the level of asset manager in the applicable Party's management
structure.

"LEASE AGREEMENT" means the oil, gas and mineral lease from Unocal to Buyer
with respect to Parachute Creek, Colorado, in the form of Exhibit "I" attached
hereto.

"LEASEHOLD INTERESTS" means the Assets described in Section 2.1(i).



                                       5

<PAGE>   14





"LIENS" means any and all liens, mortgages, charges, pledges, security
interests, or other similar type encumbrances, including, but not limited to,
such as may arise under any contracts or judgments.

"LISBON PLANT" shall have the meaning specified in Section 2.1(iii).

"MATERIAL ENVIRONMENTAL DEFICIENCY" means a deficiency or deficiencies in the
Assets arising out of the Environmental Liabilities for which the cumulative
estimated Remediation Cost will create a liability for which Buyer will be
responsible in an amount in excess of $3,500,000 and which requires remediation
or cleanup under currently applicable Environmental Laws which remediation and
cleanup obligations are not (i) merely speculative, contingent obligations
which could arise in the future and are currently uncertain or (ii) remediation
and cleanup obligations which could be anticipated to arise upon plugging and
abandonment of the applicable assets.

"MINIMAL ENVIRONMENTAL LIABILITIES" shall have the meaning specified in Section
4.7(a)(i).

"NEGATIVE PIPELINE IMBALANCE" shall mean the (a) total quantity of Hydrocarbons
(expressed in MMBtus) by which the cumulative total receipts of Hydrocarbons
from a shipper on the Pipeline Assets exceeds the cumulative total deliveries
of Hydrocarbons to the shipper on the Pipeline Assets, determined as of the
Effective Date, and (b) the total quantity of Hydrocarbons (expressed in
MMBtus) by which the total cumulative nominated and confirmed deliveries of
Hydrocarbons to an interconnected third party pipeline on the Pipeline Assets
exceeds the total cumulative actual deliveries of Hydrocarbons to the
interconnected third party pipeline on the Pipeline Assets, as of the Effective
Date.

"NORM" means naturally occurring radioactive material.

"OIL AND GAS PROPERTIES" means the Assets described in Section 2.1(ii).

"PARTY" or "PARTIES" means Unocal or TBI, or Unocal and TBI respectively.

"PARTY ADVERSE EFFECT" shall mean an event, taking into account all facts and
circumstances, on the business, properties, condition (financial or otherwise)
or operations of a Party, which has had or could reasonably be expected to have
a material adverse effect on the ability of such Party to perform its
obligations under this Agreement.

"PERMITS" means any and all permits, including temporary permits to construct
or operate, authorizations, approvals, registrations, rights of way, orders,
waivers, variances or other licenses issued or granted by any federal, state,
tribal or local administrative or governmental authority, bureau or agency.



                                       6

<PAGE>   15





"PERMITTED ENCUMBRANCES" means (i) liens for taxes, assessments or other
governmental charges or levies not yet delinquent; (ii) liens in connection
with workers' compensation, unemployment insurance or other social security,
old-age pension or public liability obligations which are not yet due or
delinquent; (iii) liens in favor of vendors, carriers, warehousemen, repairmen,
mechanics, workmen, materialmen, construction or similar liens arising by
operation of law in the ordinary course of business as to obligations which are
not yet delinquent or which have not been filed pursuant to law; (iv) rights to
consent by, required notices to, filing with, or other actions by governmental
entities in connection with the sale or conveyance of the applicable property
if the same are customarily obtained subsequent to such sale or conveyance; (v)
easements, rights of way, restrictions, encroachments and other similar
encumbrances, and minor defects in the chain of title which do not materially
interfere with the continued current use of the applicable property or
materially detract from the value of such property; (vi) rights of utility
companies to lay, maintain and repair pipelines, conduits, cable boxes and
other installations on, under, and across the applicable property; (vii) rights
reserved to or vested in any municipality or governmental, statutory or public
authority to control or regulate any interest in any manner, and all applicable
laws, rules and orders of such authority; (viii) any Lien or encumbrance in the
form of a judgment secured by a supersedeas bond or other security approved by
a court of competent jurisdiction; and (ix) all matters disclosed in the Unocal
Disclosure Schedule or Environmental Disclosure Schedule which affect the
quality or quantity of title.

"PERSON" means any individual, partnership, joint venture, firm, corporation,
association, trust, limited liability company, estate, unincorporated
organization or other entity, and their successors and assigns; or any
governmental or political subdivision, including any agency, department or
instrumentality thereof.

"PIPELINE ASSETS" shall have the meaning specified in Section 2.1(ix).

"PIPELINE IMBALANCE" shall mean the net pipeline imbalance position of the
Company (expressed in MMBtus) taking into consideration the Positive Pipeline
Imbalance and the Negative Pipeline Imbalance.

"PLUGGING AND ABANDONMENT OBLIGATIONS" means all usual and normal prudent
operations for the plugging, abandonment, surface restoration, site clearance,
and disposal of related waste materials, including NORM and asbestos, of all
oil, gas injection, water or other wells, sumps, pits, ponds, tanks,
impoundments, foundations, pipelines, structures and equipment of any kind or
description on the Assets, in compliance with all applicable contractual
obligations and applicable rules and regulations of governmental bodies having
jurisdiction over the Assets. Plugging and Abandonment Obligations do not
include cleanup of polluted lands, air or water other than routine cleanup
normally associated with plugging and abandonment, such cleanup obligations
which are other than routine being included within the definition of
Environmental Liabilities.



                                       7

<PAGE>   16





"POSITIVE PIPELINE IMBALANCE" shall mean (a) the total quantity of Hydrocarbons
(expressed in MMBtus) by which the cumulative total deliveries of Hydrocarbons
to a shipper on the Pipeline Assets exceeds the total cumulative receipts of
Hydrocarbons from the shipper on the Pipeline Assets, determined as of the
Effective Date and (b) the total quantity of Hydrocarbons (expressed in MMBtus)
by which the total cumulative actual deliveries of Hydrocarbons to an
interconnected third party pipeline on the Pipeline Assets exceeds the total
cumulative nominated and confirmed deliveries of Hydrocarbons to the
interconnected third party pipeline on the Pipeline Assets, determined as of
the Effective Date.

"PRE-EFFECTIVE DATE ROYALTIES AND TAX PAYMENTS" means all obligations, duties
or liabilities for the payment of royalties and taxes in respect of oil and gas
production from the Assets (including penalties and interest relating thereto)
which Accrued and are attributable to periods prior to the Effective Date.

"PURCHASE PRICE" shall have the meaning specified in Section 2.3.

"QUALIFIED CLAIM" means an unknown Environmental Liability which Accrued prior
to the Effective Date, and which is the subject of a specific written claim
asserting Unocal's or TBI's responsibility made and asserted during the twelve
(12) month period following the Closing Date either by a governmental entity or
by a third party that is not an Affiliate of TBI with a Claim Notice provided
by TBI to Unocal at once but in no case later than thirty (30) days after TBI's
receipt of such claim; provided, however, Environmental Law for purposes of
determining Environmental Liabilities that can be Qualified Claims shall not
include Environmental Laws as they may be amended, varied or modified in the
future, but shall be limited to Environmental Laws in effect and applicable to
the Assets as of the Effective Date.

"QUALIFIED CLAIM COST SHARING ALLOCATION" shall have the meaning specified in
Section 4.7(a).

"REMEDIATION COST" means the cost to remedy or satisfy any Environmental
Liability using the most cost effective methods and manner that satisfy
applicable Environmental Laws, and which are consistent with the continued use
of the affected Assets in the same capacity and for the same purposes as they
were being used on the Effective Date.

"SHARES" shall have the meaning specified in Section 2.3.

"STOCK OWNERSHIP AND REGISTRATION RIGHTS AGREEMENT" shall mean Exhibit "J" to
this Agreement

"SURFACE ACCESS AGREEMENTS" means the Assets described in Section 2.1(viii).

"TBI" means Tom Brown, Inc.



                                       8

<PAGE>   17





"TBI BALANCE SHEET" means the consolidated balance sheet of TBI as of December
31, 1998 set forth in the TBI annual report on Form 10-K for the year ended
December 31, 1998.

"TBI BALANCE SHEET DATE" means December 31, 1998.

"TITLE DEFECT" shall have the meaning specified in Section 3.2.

"UNOCAL" means Union Oil Company of California.

"UNOCAL DISCLOSURE SCHEDULE" means Exhibit "D" to this Agreement.

"WELLS" means all oil, condensate or natural gas wells located on the Leasehold
Interests and the Oil and Gas Properties, whether producing, shut-in or
temporarily abandoned.

1.2      UNDEFINED FINANCIAL ACCOUNTING TERMS: Undefined financial accounting
         terms used in this Agreement shall be defined according to generally
         accepted accounting principles.

1.3      REFERENCES: References in this Agreement to Sections or Exhibits shall
         be to the entirety of the Sections or Exhibits of this Agreement which
         are referred to unless expressly limited to a sub-Section in the
         reference. References, if any, in this Agreement to "hereby",
         "herein", "hereinabove", "hereinafter", "hereinbelow", "hereof",
         "hereunder", and words of similar import shall be to this Agreement in
         its entirety and not only to the particular Section or Exhibit in
         which such reference appears unless expressly stated to the contrary.

1.4      CONSTRUCTION: Unless the context otherwise requires: (i) "or" is not
         exclusive; (ii) words used in the singular include the plural and
         words used in the plural include the singular; (iii) words used in the
         masculine include the feminine and words used in the feminine include
         the masculine; (iv) any date specified for any action that is not a
         business day as such term is generally defined in the United States of
         America shall be deemed to mean the first business day after such
         date; (v) neither the captions to Sections or paragraphs hereof nor
         the Table of Contents shall be deemed to be a part of the Agreement;
         (vi) the Exhibits form a part of the Agreement and shall have the same
         force and effect as if set out in the body of the Agreement; and (vii)
         references herein to any other agreement or instrument shall, unless
         the context otherwise requires or specifies, be deemed references to
         that agreement or instrument as it may from time to time be changed,
         amended or extended, but shall not be an incorporation by reference
         unless specifically so provided.



                                       9

<PAGE>   18

                                   SECTION 2

                               PURCHASE AND SALE

2.1      ASSETS: Subject to the terms and conditions of this Agreement, Unocal
         shall sell and shall cause Pipeline (as applicable) to sell and TBI
         shall purchase on the Closing Date, effective as of the Effective
         Date, without warranty of title, either express or implied, all of
         Unocal's and Pipeline's right, title and interest in the following
         assets (collectively, the "Assets"):

         (i)   the units, prospects and fields together with the oil, gas and
               other mineral leases described in Schedule 2.1(i) insofar as
               same cover and affect the lands described in Schedule 2.1(i),
               including, but not limited to, working interests, overriding
               royalty interests, royalty interests, reversionary interests,
               net profit interests, net revenue interests, fee mineral estate
               interests and any other interests of a similar nature with
               respect to the oil, gas and other mineral leases referenced on
               Schedule 2.1(i) (it being the intent of the parties that TBI
               receive all of Unocal's ownership in such leasehold interests
               even though Unocal's interest in such units, prospects and
               fields and oil and gas and other mineral leases may be
               incorrectly described on or inadvertently omitted from Schedule
               2.1(i)) (the "Leasehold Interests");

         (ii)  producing and non-producing wells, saltwater disposal wells,
               other wells or other oil and gas properties located on or
               attributable to the Leasehold Interests, including, but not
               limited to, those described on Schedule 2.1(ii) ("Oil and Gas
               Properties");

         (iii) the Lisbon gas processing and treatment plant and the related
               lands, as described on Schedule 2.1(iii) (the "Lisbon Plant");

         (iv)  the equipment and facilities permanently located on the lands
               described in Sections 2.1(i) and 2.1(ii) or lands pooled or
               unitized therewith including, but not limited to, pumps, surface
               and subsurface well equipment, gas plants, lines and facilities,
               sulfur recovery facilities, compressors, compressor stations,
               dehydration facilities, treating facilities, gathering lines,
               flow lines, valves, meters, separators, tanks, tank batteries,
               and other fixtures (which along with the Lisbon Plant are
               collectively referred to as the "Facilities");

         (v)   the gas, oil, condensate and natural gas liquids produced after
               the Effective Date, including line fill below the pipeline
               connections as of the Effective Date attributable to the
               Leasehold Interests and the Oil and Gas Properties;

         (vi)  all equipment, personal property, warehouse stock and idle
               equipment used solely or held for use in connection with or
               charged to any of the Leasehold Interests or Oil


                                       10

<PAGE>   19





               and Gas Properties, including, without limitation, the items and
               equipment described in Schedule 2.1(vi) ;

        (vii)  all contracts and agreements concerning the properties
               described in Sections 2.1(i), 2.1(ii), 2.1(iii), 2.1(iv) and
               2.1(vi), including, but not limited to, unit agreements, pooling
               agreements, areas of mutual interest agreements, farmout
               agreements, farmin agreements, saltwater disposal agreements,
               water injection agreements, line well injection agreements, road
               use agreements, drilling contracts, operating agreements, well
               service contracts, production sales contracts, gas contracts,
               gas balancing agreements, storage or warehouse agreements,
               supplier contracts, service contracts, construction agreements,
               division orders and transfer orders, insofar as and only insofar
               as they relate to the interests and properties described in
               Sections 2.1(i), 2.1(ii), 2.1(iii), 2.1(iv) and 2.1(vi)
               ("Contract Rights");

        (viii) all surface use agreements, easements, rights of way,
               licenses, authorizations, Permits, and similar rights and
               interests applicable to, or used in connection with, any or all
               of the interests and properties described in Sections 2.1(i),
               2.1(ii), 2.1(iii) and 2.1(iv), including, without limitation,
               those items listed on Schedule 2.1(i) ("Surface Access
               Agreements");

        (ix)   that certain pipeline known as the Aneth Line consisting of
               approximately 66 miles of ten-inch diameter pipe, including
               certain pipelines, tanks, facilities and equipment as described
               in Schedule 2.1(ix), together with easements, rights of way and
               interests directly attributable thereto (collectively, "Pipeline
               Assets");

        (x)    the Lease Agreement;

        (xi)   the net cash proceeds, if any, actually received by Unocal (with
               respect to any claim respecting an event which occurred between
               the Effective Date and the Closing Date) under any policy or
               agreement of insurance or indemnity in favor of Unocal covering
               such claim;

        (xii)  the vehicles and rolling stock described on Schedule 2.1(xii);
               and

        (xiii) those certain term royalties respecting certain Parachute
               Creek properties as described on Exhibit F-3 which will be in a
               form to be mutually agreed by the parties.

2.2  EXCLUDED ASSETS: It is specifically agreed that Unocal is not selling and
     Buyer is not purchasing the following assets ("Excluded Assets"):



                                       11

<PAGE>   20





        (i)    all rights and interests of any kind in leases and lands other
               than the Leasehold Interests and Oil and Gas Properties;

        (ii)   any and all interests in the Assets Unocal is legally or
               contractually restricted from selling which are listed on
               Schedule 2.2(ii);

        (iii)  all materials and equipment leased (other than contractual
               lease rights pursuant to any lease included in the Contract
               Rights) or temporarily located on the Leasehold Interests, and
               any materials, equipment, pipelines, facilities or interests in
               the land owned by a purchaser and/or transporter of oil and/or
               gas therefrom, a lessor, or a third Person;

        (iv)   all interests in pipelines, facilities, contract rights and
               surface access agreements owned by Unocal that are not used in
               connection with the Assets or which cover lands described in the
               Leasehold Interests and Oil and Gas Properties, but which are
               used solely in connection with properties that are not being
               sold under the terms of this Agreement;

        (v)    any right to use the "Unocal" name, marks, trade dress or
               insignia, or to use the name of any other subsidiary of Unocal
               Corporation; and all of Unocal's and its Affiliates'
               intellectual property, including, but not limited to patents,
               trade secrets and copyrights other than intellectual property
               included in the Assets;

        (vi)   all amounts due or payable to Unocal or its Affiliates as
               adjustments or refunds under any contracts affecting the Assets
               and Accruing for all periods of time prior to the Effective
               Date, specifically including, without limitation, amounts
               recoverable from audits under operating agreements;

        (vii)  all rights, titles, claims and interests of Unocal and its
               Affiliates Accruing prior to the Effective Date to or under any
               policy or agreement of insurance or indemnity, any bond, or to
               any insurance proceeds or awards; and any employment,
               consulting, office lease or accounting service contracts;

        (viii) all claims and choses in action of Unocal and its Affiliates
               arising from acts, omissions or events, or damages to or
               destruction of property related to the ownership or operation of
               the Assets and Accruing prior to the Effective Date;

        (ix)   all proceeds, benefits, income or revenue Accruing to the Assets
               prior to the Effective Date, and any claims of Unocal and its
               Affiliates for refunds of or losses carried forwarded with
               respect to taxes attributable to the Assets for any period prior
               to the Effective Date; and


                                       12

<PAGE>   21





         (x)   all geophysical, geological and seismic data, surveys, analysis
               and similar data or information, and all rights therein other
               than as specifically licensed under the Geophysical Data
               Licensing Agreement.

2.3      PURCHASE PRICE: The Purchase Price ("Purchase Price") for the Assets
         shall be (i) 5,800,000 shares (the "Shares") of Common Stock as
         increased to reflect any stock dividend or other adjustment in the
         Common Stock and (ii) the cash amount of $5,000,000, which is subject
         to adjustment as set forth in Sections 2.5 and 2.6.

2.4      PAYMENT PROCEDURES:  Payment shall be made as follows:

         (i)      at Closing, TBI shall pay to Unocal an amount equal to the
                  Adjusted Cash Purchase Price, plus or minus any Cash
                  Settlement (to the extent same is a positive number) by wire
                  transfer of immediately available funds as specified by
                  Unocal;

         (ii)     at Closing, Unocal shall pay to TBI an amount equal to the
                  Adjusted Cash Purchase Price, plus or minus any Cash
                  Settlement (to the extent same is a negative number) by wire
                  transfer of immediately available funds as specified by TBI;
                  and

         (iii)    at Closing, TBI will deliver to Unocal a stock certificate
                  representing the Shares with all taxes, direct or indirect,
                  attributable to the transfer of such Shares paid or provided
                  for.

2.5      ADJUSTED CASH PURCHASE PRICE: The cash portion of the Purchase Price
         shall be adjusted as follows and the resulting amount shall be called
         the "Adjusted Cash Purchase Price":

         (i)      plus or minus any adjustments for Title Defects; minus

         (ii)     the Allocated Value of any part of the Assets sold to a third
                  Person pursuant to the exercise of a preferential purchase
                  right; plus

         (iii)    the Geophysical Seismic Licensing Price; plus or minus

         (iv)     the value of the Gas Imbalance and Pipeline Imbalance shown
                  on Schedule 6.6, as calculated pursuant to Section 10.3
                  hereof.

2.6      CASH SETTLEMENT: The sum ("Cash Settlement") due to settle accounts
         until the Final Accounting shall be determined by Unocal for Closing
         purposes by adding or subtracting from the Adjusted Cash Purchase
         Price as follows (and to the extent that such adjustments involve
         estimates or unliquidated amounts, then such estimates and
         unliquidated amounts shall be mutually agreed to by the parties not
         less than three (3) days prior to the Closing):


                                       13

<PAGE>   22





         (i)      add the amount of expenditures (or estimated expenditures as
                  agreed) made by Unocal that are attributable to the Assets
                  for the period between the Effective Date and Closing Date
                  including, without limitation, royalties, taxes, rentals and
                  similar charges and expenses, including those billed under
                  applicable operating agreements, and all prepaid expenses;

         (ii)     subtract the amount of revenues (or estimated revenues as
                  agreed) received by Unocal in connection with sales of
                  Hydrocarbons and associated products from the Assets,
                  together with any other income from the Assets, Accruing
                  after the Effective Date, excluding revenues (or estimated
                  revenues as agreed) from the sale of liquid Hydrocarbons in
                  storage tanks above the pipeline connection on the Effective
                  Date valued at market or contract prices in effect as of the
                  Effective Date after deducting royalty and tax obligations;

         (iii)    add the sum of $15,000 per month for each month or portion
                  thereof from the Effective Date to the Closing Date as
                  compensation or reimbursement to Unocal for its
                  administrative costs incurred in issuing royalty and rental
                  checks and continuing to perform accounting obligations for
                  the Assets; and

         (iv)     add the sum of $7,260 per month for each month or portion
                  thereof from the Effective Date to the Closing Date as
                  compensation or reimbursement to Unocal for assuming the risk
                  of Casualty Loss in respect of the Assets until the Closing
                  Date.

2.7      ASSUMPTION AGREEMENT: At the Closing, Buyer shall be deemed to have
         assumed the Assumed Liabilities and shall enter into an Assumption
         Agreement to acknowledge its assumption of the Assumed Liabilities.

                                   SECTION 3

                               TITLE EXAMINATION

3.1      ACCESS TO TITLE INFORMATION: After the date of this Agreement and
         until the end of the Due Diligence Period, Unocal shall make all of
         its land records that are not privileged or confidential available to
         Buyer at Unocal's offices located at 14141 Southwest Freeway, Sugar
         Land, Texas 77478, or such other place as deemed appropriate by
         Unocal, during normal business hours for examination by Buyer. Unocal
         shall not be obligated to perform any title work and no abstracts or
         title opinions will be made current by Unocal. NO WARRANTY OF ANY KIND
         IS MADE BY UNOCAL AS TO THE INFORMATION SO SUPPLIED, AND BUYER AGREES
         THAT ANY CONCLUSIONS DRAWN THEREFROM SHALL BE THE RESULT OF ITS OWN
         INDEPENDENT REVIEW AND JUDGMENT. SUBJECT TO THE OTHER PROVISIONS OF
         THIS AGREEMENT,


                                       14

<PAGE>   23





         BUYER ASSUMES THE RISK OF ANY TITLE DEFECTS AND/OR CONFLICTING ADVERSE
         RIGHT(S), TITLE(S) AND/OR INTEREST(S) WHICH A RECORD TITLE CHECK
         AND/OR PHYSICAL INSPECTION REVEALS OR WOULD HAVE REVEALED.

3.2      TITLE DEFECTS: For purposes of this Agreement, a defect in title
         ("Title Defect") shall mean a defect (other than a Permitted
         Encumbrance) in one or more of the following respects only:

         (i)      Unocal's interest in any one or more of the properties
                  comprising the Assets described in Schedules 2.1(i), 2.1(ii)
                  and 2.1(iii) is more or less than the interest for such
                  property(ies) reflected in Schedules 2.1(i), 2.1(ii) and
                  2.1(iii);

         (ii)     Unocal's rights and interests in one or more of the
                  properties comprising the Assets described in Schedules
                  2.1(i) and 2.1(ii) are subject to being reduced by virtue of
                  the exercise by a third party of a reversionary, back-in or
                  similar right not reflected in Schedules 2.1(i) and 2.1(ii)
                  nor disclosed to TBI in the Unocal Disclosure Schedule;

         (iii)    Unocal's title to one or more of the Leasehold Interests and
                  Oil and Gas Properties is such that Unocal does not have
                  Defensible Title;

         (iv)     Consents to transfer or other similar approvals, other than
                  consents or approvals which are obtained prior to Closing or
                  of a type customarily obtained following the Closing; or

         (v)      Under the Lease Agreement, Unocal is leasing to TBI less than
                  29,000 net acres.

3.3      NOTICE OF TITLE DEFECT: Upon discovery of a Title Defect, the Party
         discovering same shall as soon as reasonably possible thereafter
         notify the other Party of the Title Defect. The notice shall include
         with reasonable specificity the property or properties described in
         Schedule 2.1(i), Schedule 2.1(ii) or Schedule 2.1(iii) which are
         affected, the particular Title Defect claimed, and the notifying
         Party's good faith estimate of the Claim Value or Defect Value. Any
         Title Defect which is not asserted by Unocal or Buyer prior to the end
         of the Due Diligence Period shall conclusively be deemed waived by
         both Parties for all purposes.

3.4      CLAIM VALUE: If a claim of Title Defect is made pursuant to Section
         3.2(i) or (ii), the value of the claim ("Claim Value") shall be
         calculated using the Claim Value Formula and Allocated Values set out
         in Exhibit "A."

3.5      DEFECT VALUE: If a claim of Title Defect is made pursuant to Section
         3.2(iii) for a matter not covered by Sections 3.2 (i) or (ii), the
         value of the defect ("Defect Value") for a defect that is a liquidated
         or certain amount shall be such liquidated or certain amount, and as
         to


                                       15

<PAGE>   24





         unliquidated or uncertain amounts it shall be an amount necessary to
         compensate Buyer for the adverse economic effect of such Title Defect
         on the value of the property(ies) affected, taking into consideration
         all relevant factors, including the practical and legal effect of the
         Title Defect. In no instance shall a Defect Value be an amount in
         excess of the Allocated Value of an affected property.

3.6      REMEDIES FOR TITLE DEFECTS:

         (i)   Prior to the Closing Date, Unocal may elect to cure any or all
               Title Defects; provided, however, if Unocal elects to cure a
               Title Defect, but has not been able to do so by the Closing
               Date, the Parties shall proceed with the Closing, with the Claim
               Value or Defect Value, as applicable, being an adjustment to the
               Purchase Price. Unocal shall retain the right to cure any such
               Title Defect for a period of time not to exceed one hundred
               eighty (180) days after the Closing Date. Within thirty (30)
               days of Buyer's receipt of curative documents which eliminate
               the Title Defect, Buyer shall tender to Unocal the applicable
               Claim Value or Defect Value withheld at Closing. Unocal's option
               to cure Sections 3.2 (i) or (ii) Title Defects shall include the
               option to partially cure any such Title Defect or Title Defects
               so as to reduce the Claim Value of the Title Defect or Title
               Defects.

         (ii)  If the Claim Value or Defect Value of a Title Defect is equal to
               twenty-five percent (25%) or more of the Allocated Value of a
               property described in Schedule 2.1(i) or 2.1(ii), Unocal may in
               its sole discretion elect to retain the affected property and
               delete it from the Assets. In such instance, the Adjusted Cash
               Purchase Price shall be adjusted downward in an amount equal to
               the Allocated Value of the retained property(ies).

         (iii) If a Title Defect is a Section 3.2(i) or (ii) Title Defect
               which increases or decreases Unocal's interest in the Assets,
               and Unocal does not elect to cure the Title Defect, the Adjusted
               Cash Purchase Price shall be adjusted up or down by the Claim
               Value of the Title Defect.

         (iv)  If Unocal contests the existence of a Title Defect or Buyer's
               good faith estimate of the Claim Value or Defect Value of the
               Title Defect, the Parties shall meet and use their best efforts
               to agree on the validity and/or value of the Title Defect. If
               the Parties cannot agree on the validity and/or value of a Title
               Defect, and neither Party elects to waive its claim, the dispute
               shall be submitted to arbitration in accordance with the
               arbitration procedures set forth in Exhibit "B."



                                       16

<PAGE>   25





         (v)   If Unocal agrees, or is required, to pay the Claim Value of the
               Title Defect, it shall pay the Claim Value of the Title Defect
               by an adjustment to the Adjusted Cash Purchase Price by the
               Claim Value of the Title Defect.

3.7      PURCHASE PRICE ADJUSTMENTS THRESHOLD: Notwithstanding any other
         provision herein, the Purchase Price shall not be adjusted due to or
         for a Title Defect, and neither Party shall notify the other Party of
         a Title Defect unless or until the Claim Value or Defect Value of the
         Title Defect exceeds a minimum threshold of $25,000. This $25,000
         Title Defect threshold shall be applied separately to each property
         described in Schedules 2.1(i) or 2.1(ii) that has been assigned a
         separate Allocated Value, but Title Defects shall be calculated on a
         cumulative basis if a separate property is subject to more than one
         Title Defect. If the aggregate total of Title Defects exceeds
         $7,000,000, then Buyer may terminate this Agreement pursuant to
         Section 13.1(ii).

3.8      PREFERENTIAL PURCHASE RIGHTS: (a) Preferential purchase rights shall
         not be considered Title Defects hereunder regardless of whether or not
         they are reflected in the Unocal Disclosure Schedule. As to any and
         all preferential purchase rights known to Unocal prior to the Closing
         affecting Unocal's or its Affiliates' interest in all or part of the
         Assets, in accordance with the provisions of the agreement which
         created the rights, Unocal shall send, as soon as practicable after
         execution of this Agreement, to the owner or owners of such rights a
         notice offering to sell to such owner or owners, those Assets covered
         by such rights for the Allocated Value assigned to the affected
         Assets. If the owner or owners of the rights exercise such rights
         prior to Closing, the affected portion of the Assets shall be deleted
         from the transaction, and the Adjusted Cash Purchase Price shall be
         reduced in an amount equal to the Allocated Value of the deleted
         Assets; provided, however, that Buyer, at its sole expense, shall have
         the right to challenge the asserted preferential rights (and shall
         indemnify, defend, and hold harmless Unocal from claims, damages and
         liabilities arising therefrom or relating thereto). If the specific
         Assets affected do not have a separate Allocated Value, the value
         shall be the Claim Value of the deleted Assets. The Assets which are
         known by Unocal to be subject to preferential purchase rights are
         listed on Schedule 3.8. By listing Assets on Schedule 3.8, Unocal does
         not admit, warrant or represent that any of such Assets are subject to
         preferential purchase rights which have not been waived or that such
         listing is an exhaustive list of all preferential purchase rights
         affecting the Assets. To the extent and in the manner required under
         applicable agreements, Unocal shall either comply with each
         preferential purchase right listed on Schedule 3.8 or obtain a waiver
         thereof. Unocal may seek and obtain waivers of any applicable or
         purported preferential purchase right, in a commercially reasonable
         manner discharging the obligations required of Unocal.

         (b) If the holder of a preferential purchase right fails to consummate
         the purchase of the Assets covered by such right after notice of
         exercise, then Unocal shall so notify Buyer, and


                                       17

<PAGE>   26





         Buyer shall purchase from Unocal, for a price equal to the Allocated
         Values and upon the other terms of this Agreement, the Assets to which
         the preferential purchase right applied. All Assets for which a
         preferential purchase right has not been asserted prior to Closing
         shall be sold to Buyer at Closing pursuant to the provisions of this
         Agreement. If one or more of the holders of such preferential purchase
         rights notifies Unocal subsequent to Closing that it intends to assert
         its preferential purchase right, Unocal shall give notice thereof to
         Buyer, whereupon Buyer may elect to: (i) at its sole expense, satisfy
         such preferential purchase right obligations of Unocal to such holders
         and Buyer shall be entitled to receive and Unocal hereby assigns to
         Buyer, all of Unocal's right to all proceeds received from such
         holders in connection with such preferential purchase rights or (ii)
         convey the Assets subject to the preferential purchase right to Unocal
         and Unocal shall remit to Buyer an amount equal to the Allocated Value
         of Assets. If Buyer elects to satisfy the preferential purchase right
         obligations of Unocal pursuant to subsection (i) above, then Buyer
         shall indemnify, defend and hold harmless Unocal from claims, damages
         and liabilities arising therefrom or relating thereto. If Buyer elects
         to convey Assets to Unocal pursuant to subsection (ii) above, then
         Buyer agrees to make such decision and conveyance promptly following
         Buyer's becoming aware of the preferential purchase right (and in no
         case more than ten (10) days following notice to Buyer that such
         preferential right is being asserted) so that Unocal will have
         adequate reasonable opportunity and time to challenge or satisfy the
         preferential purchase rights subject to such notification.

3.9      PREFERENTIAL PURCHASE RIGHT DISPUTES: (i) If an owner of a preferential
         purchase right obtains judicial relief which permanently enjoins the
         consummation of the transactions contemplated under this Agreement or
         enjoins the transfer of Assets representing in excess of 20% of the
         Purchase Price, such enjoinder shall be deemed a termination of this
         Agreement by mutual consent of the Parties.

         (ii) If, following the Closing, an owner of a preferential purchase
right (including any Preferential Right which was not listed on Schedule 3.8)
seeks judicial relief, which may include injunctive relief, and Buyer elects
not to re-convey the affected Assets under Section 3.8(b) above or the time
period to re-convey the affected Assets under Section 3.8(b) above has
otherwise expired, then Buyer shall indemnify, defend and hold Unocal harmless
from any and all claims, causes of action, costs and expenses arising out of or
relating to such dispute.

                                   SECTION 4

                             ENVIRONMENTAL MATTERS

4.1      NO ADMISSION AGAINST INTEREST: Nothing contained in this Section 4, or
         elsewhere in this Agreement, shall be construed to be an admission
         against interest as to Unocal or TBI. Unocal and TBI have not included
         Environmental Liability related provisions herein due to


                                       18

<PAGE>   27





         any perceived liability and specifically disclaim the existence of any
         such liability to third parties (including governmental entities)
         based on contract, tort, statute or otherwise.

4.2      PHYSICAL CONDITION OF THE ASSETS: Buyer acknowledges that the Assets
         have been used for oil and gas drilling and production operations, gas
         processing operations, related oil field operations and possibly for
         the storage and disposal of Deleterious Substances, and the Assets may
         be contaminated with such materials. Physical changes in or under the
         Leasehold Interests, Oil and Gas Properties or adjacent lands may have
         occurred as a result of such uses. The Assets may contain wells,
         sumps, landfills, pits, ponds, tanks, impoundments, foundations,
         pipelines and other equipment, whether or not of a similar nature, any
         of which may be buried and contain Deleterious Substances, and the
         locations of which may not be known to Unocal or be readily apparent
         by a physical inspection of the property. Further, spills, leaks,
         blowouts and routine operations may have led to contamination of the
         Assets with Deleterious Substances, the locations of which may not be
         known to Unocal or be readily apparent by a physical inspection of the
         property. Buyer understands that Unocal does not have the requisite
         information with which to determine the exact nature or condition of
         the Assets nor the effect any use has had on the physical condition of
         the Assets. In addition Buyer acknowledges that some oil field
         production equipment may contain asbestos and/or NORM. In this regard,
         Buyer expressly understands that NORM may affix or attach itself to
         the inside of wells, materials and equipment as scale or in other
         forms, and that wells, materials and equipment located on the Assets
         described herein may contain asbestos and NORM, and that NORM in the
         form of scale or in other forms may have become dislodged from the
         inside of wells, materials and equipment and be located on the Assets
         and that asbestos and NORM containing materials may be buried or have
         been otherwise disposed of on the Assets. Buyer also expressly
         understands that special procedures may be required for the removal
         and disposal of asbestos, NORM, and other Deleterious Substances from
         the Assets where they may be found.

4.3      ENDANGERED SPECIES, CRITICAL HABITAT, WETLANDS, GEOLOGIC HAZARDS AND
         FLOODING: "Endangered Species" as used herein shall have the same
         meaning as "endangered species" is defined pursuant to 16 U.S.C.
         1532(6) or the laws of the state in which the Leasehold Interest is
         located; as "threatened species" is defined pursuant to 16 U.S.C.
         1533(30) or the laws of the state in which the Leasehold Interest is
         located; and/or, as a candidate species for such listing under federal
         or state law. "Critical Habitat" as used herein shall have the meaning
         as defined pursuant to 16 U.S.C. 1532(5). "Wetland" as used herein
         shall have the meaning as defined in 40 Code of Federal Regulations
         ss.230.3(a), or under the laws of the state in which the Leasehold
         Interest is located. "Geologic Hazards" as used herein shall include
         seismic hazard and any earth slides or other earth movement.
         "Flooding" as used herein shall include the risks associated with a
         flood plain, flood way or restriction zone and/or any diminution in
         the value of the Property or restriction of its use by reason of the
         risk of water entering or remaining thereon. WITHOUT IN ANY WAY
         LIMITING ANY


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<PAGE>   28





         OTHER DISCLAIMERS OF WARRANTY HEREIN AND NOTWITHSTANDING ANY
         DISCLOSURES MADE BY UNOCAL TO BUYER, UNOCAL AND ITS AFFILIATES
         DISCLAIM ANY EXPRESS OR IMPLIED WARRANTY OR REPRESENTATION AS OF THE
         DATE OF THIS AGREEMENT AND/OR AS OF THE CLOSING OF THE COMPLETENESS OF
         ANY SUCH DISCLOSURE OR THAT THE ASSETS ARE FREE FROM ANY ENDANGERED
         SPECIES OR THAT ALL OR ANY PART OF THE ASSETS ARE NOT A CRITICAL
         HABITAT OR A WETLAND, OR THAT ANY PART OF THE ASSETS DOES NOT INCLUDE
         A GEOLOGIC HAZARD, OR THAT ANY PART OF THE ASSETS ARE NOT SUBJECT TO
         FLOODING. Notwithstanding any
         knowledge that could be imputed to Unocal or its Affiliates, Buyer has
         the obligation to ascertain the presence of and extent of any
         Endangered Species, Critical Habitat, Wetland, Geologic Hazards and
         the risk of Flooding on the Assets.

4.4      ENVIRONMENTAL ASSESSMENTS AND COMPLETION OF ENVIRONMENTAL DUE
         DILIGENCE: From the date of this Agreement, Unocal will provide TBI
         (or its contractor) with reasonable access to certain employees of
         Unocal, certain records of Unocal and the Assets operated by Unocal
         for the Due Diligence Period, during which TBI will, as part of TBI's
         due diligence, conduct, at its sole risk and expense, Phase I
         environmental site assessments as provided below and such additional
         environmental site assessments as are commercially reasonable under
         the circumstances and as TBI and Unocal determine is appropriate
         (collectively, the "Environmental Assessments"). In the event the
         Parties (acting in good faith) cannot agree to the terms of the
         preceding sentence, this Agreement shall terminate under Section
         13.1(i) of this Agreement. TBI may conduct a Phase I environmental
         site assessment (pursuant to American Society for Testing and
         Materials standards) on each of the fields operated by Unocal set
         forth in Exhibit "C" to be conducted by an unrelated third party
         qualified to conduct such Phase I environmental site assessments. TBI
         agrees to immediately provide to Unocal a copy of the Environmental
         Assessments, including all reports, data and conclusions, and, in any
         event, TBI shall provide Unocal a copy of all of the foregoing no
         later than 15 days prior to Closing and if the Closing occurs, and the
         Assets are sold and assigned to Buyer, Unocal shall keep all such
         information strictly confidential. Buyer shall keep any data or
         information acquired by all such examinations and the results of all
         analyses of such data and information strictly confidential and,
         unless required by law, will not disclose same to any person or agency
         without the prior written approval of Unocal except to the extent such
         disclosure is (i) required by applicable law or (ii) to financial
         institutions, environmental consultants, legal counsel or other
         parties to whom disclosure is appropriate and desirable to consummate
         this transaction, but subject to the prior agreement of any such party
         to maintain the confidentiality of the information. Buyer shall
         complete its environmental due diligence within the Due Diligence
         Period.


                                       20

<PAGE>   29



4.5      BUYER'S ACCESS TO ASSETS; INDEMNIFICATION; INSURANCE:


         (i)   Buyer shall have reasonable access to the Assets to conduct its
               environmental due diligence including but not limited to the
               Environmental Assessments. Buyer shall not perform any act or
               permit the performance of any act that would injure the Assets
               (other than soil sampling which is approved by Unocal in
               writing) or unreasonably disrupt Unocal's or its Affiliates'
               activities thereon or the surface owner's or the surface
               tenant's activities thereon. If the consent of the surface owner
               or the surface tenant or any other third party is required in
               connection with Buyer's access to the Assets, Buyer agrees to
               obtain such consent, with the assistance and cooperation of
               Unocal (at no cost to Unocal), before entering onto the Assets
               affected thereby.

         (ii)  BUYER RELEASES AND AGREES TO INDEMNIFY, DEFEND AND HOLD HARMLESS
               Unocal, its Affiliates, its or their directors, officers,
               employees and agents against all claims for injury to, or death
               of, persons or damage to property arising in any way from the
               exercise of access rights granted to Buyer for environmental due
               diligence or due diligence for any other purpose, or from the
               activities of Buyer or its employees, agents or contractors on
               the Assets. Buyer shall indemnify Unocal, its Affiliates, its or
               their directors, officers, employees and agents against and hold
               each and all of said indemnitees harmless from any and all loss,
               cost, damage, expense or liability, including attorney's fees,
               arising out of (i) any and all third party statutory or
               common-law Liens or other encumbrances for labor or materials
               furnished in connection with such tests, samplings, studies or
               surveys as Buyer may conduct with respect to the Assets; and
               (ii) any injury to or death of persons or damage to property
               occurring in, on or about the Assets as the result of Buyer's
               due diligence activities REGARDLESS OF THE SOLE, JOINT OR
               CONCURRENT NEGLIGENCE, STRICT LIABILITY, PREMISES LIABILITY,
               BREACH OF CONTRACT, OR OTHER FAULT OR RESPONSIBILITY OF UNOCAL
               OR ANY PARTY OR PERSON (except for any such injuries or damages
               caused solely by the gross negligence or willful misconduct of
               any said indemnitees). The foregoing obligation of indemnity
               shall survive Closing or termination of this Agreement without
               Closing.

         (iii) Buyer shall obtain and maintain or shall cause its outside
               environmental consultants, if such consultants are engaged in
               activities on the Assets, to obtain and maintain insurance
               acceptable to Unocal which is primary as to any insurance or
               self-insurance available to Unocal and which names Unocal and
               its Affiliates as additional insureds with respect to liability
               arising out of Buyer's or its agents' activities on the Assets,
               including a severability of interest clause (cross liability),
               which additional insured endorsement shall not exclude coverage
               based upon the alleged or actual negligence of the additional
               insured. Such insurance shall include:



                                       21

<PAGE>   30





                  (a)      commercial general liability insurance occurrence
                           form or the equivalent with the amendment-aggregate
                           limits of insurance covering contractual liability,
                           subcontractor's liability, blanket contractual
                           liability, and, unless waived in writing by Unocal,
                           liability arising from explosion, collapse, or
                           underground property damage, all with a minimum
                           combined single limit of $1,000,000.00 each
                           occurrence, $2,000,000.00 aggregate, for bodily
                           injury, death, property damage, business
                           interruption and personal injury;

                  (b)      comprehensive automobile liability insurance or
                           business auto policy on an occurrence basis covering
                           all owned, hired or otherwise operated non-owned
                           vehicles with a minimum combined single limit of
                           $1,000,000.00 each occurrence for bodily injury,
                           death and property damage;

                  (c)      workers' compensation insurance as required by law; 
                           and

                  (d)      employers' liability insurance with a minimum limit
                           of $1,000,000.00 each occurrence.

Such insurance shall be written by a carrier with a Best's rating of A IX or
above. Before the entry by Buyer upon the Assets, Buyer shall provide Unocal
with policies or certificates of the aforesaid insurance acceptable in form and
substance to Unocal which shall provide that coverage shall not be canceled or
materially changed prior to thirty (30) days' written notice to Unocal.
Subrogation against Unocal and its Affiliates shall be waived with respect to
all of the insurance policies set forth above (including without limitation,
policies of any consultant). The insurance required by this provision in no way
limits Buyer's obligations under any other Section of this Agreement. Further,
the insurance to be carried shall in no way be limited by any limitation
expressed elsewhere in this Agreement, or any limitation placed on the
indemnity herein given or as a matter of law.

4.6      ASSUMPTION OF ENVIRONMENTAL LIABILITIES: Buyer shall assume and
         discharge any and all Environmental Liabilities relating to or arising
         from the Assets, whether relating to or arising from ownership or
         operations before or after the Effective Date, except as follows:

         (i)      Buyer assumes no Environmental Liabilities unless and until 
                  Closing occurs; and

         (ii)     Based on the Qualified Claim Cost Sharing Allocation, Unocal
                  shall be responsible only for a portion of the Remediation
                  Costs for Qualified Claims.




                                       22

<PAGE>   31



4.7      QUALIFIED CLAIM COST SHARING:

         (a)      Any Remediation Costs incurred by Buyer or Unocal or its
                  Affiliates in satisfying a Qualified Claim shall be allocated
                  and satisfied by the Parties as follows ("Qualified Claim
                  Cost Sharing Allocation"):

                  (i)      each separate and distinct Qualified Claim for which
                           the Remediation Cost is $10,000 or less ("Minimal
                           Environmental Liabilities") shall be allocated to
                           and satisfied by Buyer;

                  (ii)     Subject to Section 4.7(a)(i) above, cumulative
                           Remediation Costs for all Qualified Claims, except
                           Minimal Environmental Liabilities, up to an
                           aggregate amount equal to $50,000 are allocated to
                           and shall be satisfied by Unocal and Buyer as
                           follows: Buyer shall satisfy the first $10,000 of
                           each separate and distinct Qualified Claim for which
                           the Remediation Cost is greater than $10,000 and
                           Unocal satisfying the balance of the claim up to an
                           aggregate amount for all Qualified Claims of
                           $50,000;

                  (iii)    Subject to Sections 4.7(a)(i) and (ii) above,
                           cumulative Remediation Costs for all Qualified 
                           Claims, except Minimal Environmental Liabilities, 
                           which exceed an aggregate amount equal to $50,000 
                           (with such aggregate $50,000 for all Qualified Claims
                           being allocated and satisfied in the manner described
                           in Section 4.7(a)(ii) above) and up to an aggregate 
                           amount equal to 26.2% of the Purchase Price (which, 
                           for purposes of this Section 4.7(a)(iii) is deemed 
                           to be $20 million based upon a Purchase Price of 
                           $76.4 million) are allocated to and shall
                           be satisfied one-half by Buyer and one-half by 
                           Unocal.

                  (iv)     Subject to Sections 4.7(a)(i) - (iii) above,
                           cumulative Remediation Costs for all Qualified
                           Claims, except Minimal Environmental Liabilities,
                           which exceed an aggregate amount equal to 26.2% of
                           the Purchase Price (which, for purposes of this
                           Section 4.7(a)(iv) is deemed to be $20 million based
                           upon a Purchase Price of $76.4 million) are
                           allocated to and shall be satisfied
                           solely by Buyer.

         (b)      An example of the application of the Qualified Claim Cost
                  Sharing Allocation is set forth on Schedule 4.7 hereto.

         (c)      NOTWITHSTANDING ANYTHING STATED HEREIN TO THE CONTRARY, THE
                  LIMITATIONS ON UNOCAL'S LIABILITY, AND THE ASSUMPTION OF ALL
                  LIABILITIES ABOVE SUCH LIMITATIONS BY BUYER, UNDER THIS
                  SECTION 4 AND ELSEWHERE IN THIS AGREEMENT SHALL APPLY
                  REGARDLESS OF WHETHER SUCH LIABILITIES ARE KNOWN OR UNKNOWN,
                  RELATE TO ACTIONS,


                                       23

<PAGE>   32





                  EVENTS OR CONDITIONS EXISTING OR OCCURRING PRIOR TO THE
                  EFFECTIVE DATE, WHETHER ATTRIBUTABLE (IN WHOLE OR IN PART) TO
                  THE ACTIONS, SOLE, JOINT OR CONCURRENT NEGLIGENCE, STRICT
                  LIABILITY, BREACH OF CONTRACT, PRODUCTS LIABILITY,
                  ENVIRONMENTAL LIABILITY, OR OTHER FAULT, LIABILITY OR
                  RESPONSIBILITY OF UNOCAL OR ANY OTHER PERSON OR PARTY, AND
                  REGARDLESS OF WHETHER ASSERTED UNDER ANY THEORY OF LIABILITY.

4.8      LIMITATION: No obligations allocated to or assumed by Unocal under
         this Agreement shall include any obligation to remediate any
         Environmental Liability in or upon land or any water course or body of
         water including ground water beyond the lawful requirements of the
         government agency or agencies with jurisdiction over the Assets or a
         court of competent jurisdiction, nor shall such obligations include
         any action, cost or expense other than actions, costs, or expenses
         required by law. Between the Parties, Unocal shall have the right but
         not the obligation to direct and control any work required to remedy
         Environmental Liabilities if it may be responsible for more than fifty
         percent (50%) of the costs and expenses of such work attributable to
         the interest of the Parties; provided, however, if the Parties have
         control, regardless of which Party directs and controls any required
         work to remedy Environmental Liabilities, all such actions shall be
         the most cost efficient possible to comply with applicable
         Environmental Laws and which are consistent with continued use of the
         Assets for the same purposes they were being used on the Effective
         Date, and shall be based on mutually acceptable actions after
         consultation with the other Party.

4.9      TERMINATION DUE TO MATERIAL ENVIRONMENTAL DEFICIENCIES: If it is
         determined during the Due Diligence Period that a Material
         Environmental Deficiency exists, either Buyer or Unocal may elect to
         terminate this Agreement, unless Buyer and Unocal mutually agree in
         writing to delete all or part of the affected Assets from this
         Agreement, and adjust the Adjusted Cash Purchase Price accordingly,
         such that the total Environmental Liabilities remaining do not
         constitute a Material Environmental Deficiency.

4.10     DETERMINATION OF VALUE:

         (i)      Upon delivery of notice by Buyer to Unocal of a Material
                  Environmental Deficiency, Buyer and Unocal shall meet and use
                  their best efforts to agree on whether such a Material
                  Environmental Deficiency exists. The value of Environmental
                  Liabilities shall be based on the estimated Remediation Cost.

         (ii)     If, during the Due Diligence Period, Buyer determines there
                  is a Material Environmental Deficiency and desires to
                  terminate this Agreement, it shall immediately so notify
                  Unocal. Unocal shall respond on the earlier of the Closing


                                       24

<PAGE>   33


                  Date or seven (7) days from the date of notice whether it
                  concurs in Buyer's determination that the estimated
                  Remediation Cost of the applicable Environmental Liabilities
                  is sufficient to constitute a Material Environmental
                  Deficiency. In the event Unocal concurs in Buyer's
                  determination, the termination of this Agreement shall be
                  treated as a termination by mutual consent of the Parties.

         (iii)    If Unocal timely notifies Buyer that it does not concur with
                  the Buyer's determination of the estimated Remediation Costs,
                  Buyer may still elect to terminate this Agreement and request
                  a determination of the value of the Environmental Liabilities
                  by the following procedure: the Parties will submit the issue
                  of the existence of a Material Environmental Deficiency to
                  arbitration in accordance with the arbitration procedures set
                  forth in Exhibit "B." If the arbitrators determine that a
                  Material Environmental Deficiency does not exist, Buyer will 
                  pay the arbitration costs. If the arbitrators find that a 
                  Material Environmental Deficiency does exist, Unocal will pay
                  the arbitration costs. If Buyer does not elect to terminate 
                  this Agreement prior to the commencement of arbitration in 
                  connection with this Section, then Buyer shall be deemed to 
                  have waived its right to terminate this Agreement under this 
                  Section unless and until the arbitrators determined that a 
                  Material Environmental Deficiency exists, and if such 
                  arbitrators determine that no Material Environmental 
                  Deficiency exists, then Buyer shall pay all arbitration costs
                  and proceed to Closing, subject to the other terms and 
                  conditions of this Agreement.

         (iv)     Any and all disagreements between Buyer and Unocal regarding
                  the value of Environmental Liabilities shall be submitted to
                  arbitration in accordance with the arbitration procedures set
                  forth in Exhibit "B."

                                   SECTION 5

                          OPERATIONS AND CASUALTY LOSS

5.1      OPERATIONS: Between the Effective Date and Closing, as to the portion
         of the Assets to be conveyed which Unocal now operates, it shall
         operate the same in a good and workmanlike manner. At Closing, such
         operations shall be turned over to and become the responsibility of
         Buyer, unless an applicable unit, pooling, communitization or
         operating agreement requires otherwise, in which case (unless Buyer
         and Unocal otherwise agree) Unocal shall continue the physical
         operation of such portion of the Assets, pursuant to and under the
         terms of such applicable agreement, until such time after Closing as
         such applicable agreement may require. However, Unocal shall have no
         liability as operator to Buyer, for any operations by Unocal, for loss
         or damages sustained, or liabilities incurred, REGARDLESS OF THE SOLE,
         JOINT OR CONCURRENT NEGLIGENCE, STRICT LIABILITY, BREACH OF CONTRACT
         OR OTHER FAULT OR RESPONSIBILITY OF


                                       25

<PAGE>   34


         UNOCAL OR ANY OTHER PERSON OR PARTY, except as may result directly from
         Unocal's gross negligence or willful misconduct. Such operations from
         and after the Closing shall be conducted by Unocal for and on behalf
         of Buyer, and Unocal shall make appropriate charges to Buyer pursuant
         to any applicable operating agreement pursuant to Sections 2.6(i),
         (iii) and (iv). In the absence of any applicable operating agreement,
         for any such services performed by Unocal as operator of the Assets
         (or portions thereof) from and after the Effective Date, Buyer shall
         pay to Unocal the applicable Asset's working interest percentage of an
         overhead operating charge of $660 per month per active well operated
         by Unocal; plus Buyer shall reimburse all reasonable and necessary
         expenses incurred by Unocal in such operation, protection or
         maintenance of the Assets as are not normally included within the
         operating charge in standard form accounting procedures but are paid
         as direct charges thereunder. Any such charges and expenses shall be
         recovered by Unocal as part of the Closing or Final Accounting
         adjustments as appropriate.

5.2      CASUALTY LOSS: Upon the Closing, the risk of Casualty Loss relating to
         the Assets shall pass from Unocal to Buyer, effective as of the
         Effective Date.

5.3      SUCCESSOR OPERATOR: Buyer acknowledges and agrees that Unocal cannot
         and does not covenant or warrant that Buyer shall become successor
         operator of all or any portion of the Assets, since the Assets or
         portions thereof may be subject to unit, pooling, communitization,
         operating or other agreements which control the appointment of a
         successor operator. Unocal agrees, however, that as to the Assets it
         operates, where it will facilitate the appointment of a successor
         operator, Unocal will use its reasonable efforts to recommend TBI as
         successor operator and will resign as operator when a successor
         operator assumes operations.

5.4      RESTRICTIONS ON OPERATIONS: Between the Execution Date and Closing,
         except as necessary in Unocal's opinion in emergency situations,
         Unocal shall not, without Buyer's consent, voluntarily incur any
         liability or enter into any commitment with respect to the Assets
         which will cost in excess of $50,000 net to Unocal with respect to an
         individual project; cancel any contract associated with the Assets
         except in the ordinary course of business; or enter into any hedging,
         forward sales or similar agreements with respect to production from
         the Assets.

5.5      PERMIT TRANSFERS: Buyer acknowledges and agrees to the following 
         regarding the transfer of Permits:

         (a)      Unocal and Buyer agree that, as of the Closing Date, Buyer
                  shall be responsible for compliance with the Permits, whether
                  or not Unocal or Buyer is the permit holder or operator under
                  the Permits. After the Closing Date, Buyer agrees to maintain
                  all Permits in full force and effect in compliance with the
                  laws applicable to such Permits.


                                       26

<PAGE>   35


         (b)      Buyer acknowledges that certain of the Permits, by their
                  terms, cannot be transferred. Buyer agrees to promptly apply
                  for and diligently pursue new Permits in all cases where a
                  Permit cannot be transferred to Buyer and Buyer and Unocal
                  agree to diligently pursue the transfer of Permits which are
                  transferable.

         (c)      Certain of the Pipeline Assets owned by Unocal are currently
                  FERC common carriage and will require FERC approval and 
                  possibly other regulatory approval prior to transfer of
                  such Pipeline Assets to Buyer. Unocal and Buyer shall
                  commence promptly and thereafter diligently pursue the
                  appropriate process necessary to gain FERC approval and
                  other regulatory approvals to transfer such Pipeline Assets
                  to Buyer. Since the FERC and regulatory approval process
                  may extend beyond Closing, Unocal shall (to the extent
                  permissable under applicable licenses, permits and
                  regulations and in accordance with a management agreement
                  to be mutually agreed upon by the parties) retain
                  operations and ownership of such Pipeline Assets until FERC
                  approval or other regulatory approvals required by Unocal
                  to transfer such Pipeline Assets to Buyer are obtained.

         (d)      After Closing and to the extent agreed in writing by Unocal,
                  Unocal will continue as permit holder on behalf of Buyer
                  under those Permits that have yet to be assigned or issued to
                  Buyer until such time as all Permits necessary to the
                  operation of the Assets and Pipeline Assets have been
                  assigned or issued to Buyer. After Closing and for as long as
                  Unocal or Unocal's name remains on a Permit, Buyer shall
                  indemnify and hold Unocal and its Affiliates harmless from
                  and against any and all claims in respect of Environmental
                  Liabilities arising out of, resulting from or relating to the
                  Permits.

         (e)      For as long as Unocal or Unocal's name remains on any Permit,
                  Buyer agrees not to sell any Assets related thereto or
                  transfer such related Permit without Unocal's prior written
                  consent, which may be given or withheld in its sole
                  discretion.

                                   SECTION 6

                    REPRESENTATIONS AND WARRANTIES OF UNOCAL

         Unocal hereby represents and warrants to Buyer as follows:

6.1      ORGANIZATION: Unocal is a corporation duly organized, validly existing
         and in good standing under the laws of the state of California, and is
         qualified to do business and is in good standing as a foreign
         corporation in every other jurisdiction where the failure to so
         qualify would have a Party Adverse Effect on Unocal.



                                       27

<PAGE>   36


6.2      AUTHORITY TO DO BUSINESS: Unocal has all requisite power and authority
         to own, lease or operate the Assets and to carry on the business as
         now conducted.

6.3      AUTHORITY; ENFORCEABILITY:

         (i)      Unocal has all requisite corporate power and authority to
                  enter into and perform its obligations under this Agreement
                  and to carry out the transactions contemplated hereby.

         (ii)     All corporate acts and other proceedings required to be taken
                  by Unocal to authorize the execution, delivery and
                  performance by Unocal of this Agreement have been duly and
                  properly taken.

         (iii)    This Agreement has been duly executed and delivered by Unocal
                  and constitutes the legal, valid and binding obligation of
                  Unocal, enforceable against Unocal in accordance with its
                  terms.

         (iv)     The execution, delivery and performance by Unocal of this
                  Agreement does not and will not conflict with, or result in
                  any violation of or default under any provision of the
                  Articles of Incorporation or By-laws of Unocal or any law,
                  ordinance, rule, regulation, judgment, order, decree,
                  agreement, instrument or license applicable to Unocal or to
                  the Assets.

6.4      LITIGATION, SUITS OR CLAIMS: Except as disclosed in the Unocal
         Disclosure Schedule, (a) there are no actions, suits or proceedings
         pending or, to Unocal's Knowledge, threatened in writing against
         Unocal which if decided unfavorably to Unocal could have a material
         adverse effect on any of the Assets (other than actions, suits,
         proceedings, asserted or threatened, relating to Title Defects or
         Environmental Liabilities or disclosed in any of the exhibits or
         schedules to this Agreement) and (b) to Unocal's Knowledge, no written
         notice from any governmental authority or person has been received by
         Unocal claiming any violation or repudiation of the Oil and Gas
         Properties or any violation of any law, rule, regulation, ordinance,
         order, decision or decree of any governmental authority (including,
         without limitation, any such law, rule, regulation, ordinance, order,
         decision or decree concerning the conservation of natural resources)
         relating to the Oil and Gas Properties.

6.5      DISCLAIMER OF WARRANTIES: EXCEPT AS HEREIN PROVIDED, SUBJECT TO
         SECTIONS 6.8 AND 6.9 HEREOF, THE ASSETS ARE SOLD "AS IS," "WHERE IS"
         AND "WITH ALL FAULTS AS TO ALL MATTERS," AND UNOCAL AND ITS AFFILIATES
         EXPRESSLY DISCLAIM AND NEGATE ANY REPRESENTATION OR WARRANTY, EXPRESS,
         IMPLIED, AT COMMON LAW, BY STATUTE, OR OTHERWISE RELATING TO (a) THE
         CONDITIONS OF THE ASSETS (INCLUDING,


                                       28

<PAGE>   37


         WITHOUT LIMITATION, ANY IMPLIED OR EXPRESS WARRANTY OF
         MERCHANTABILITY, OF FITNESS FOR A PARTICULAR PURPOSE, OR OF CONFORMITY
         TO MODELS OR SAMPLES OF MATERIALS), (b) ANY INFRINGEMENT BY UNOCAL OF
         ANY PATENT OR PROPRIETARY RIGHT OF ANY THIRD PARTY, (c) ANY
         INFORMATION, DATA OR OTHER MATERIALS (WRITTEN OR ORAL) FURNISHED TO
         BUYER BY OR ON BEHALF OF UNOCAL (INCLUDING WITHOUT LIMITATION, IN
         RESPECT OF GEOLOGICAL AND ENGINEERING DATA, THE EXISTENCE OR EXTENT OF
         OIL, GAS OR OTHER MINERAL RESERVES, THE RECOVERABILITY OF OR THE COST
         OF RECOVERING ANY SUCH RESERVES, THE VALUE OF SUCH RESERVES, ANY
         PRODUCT PRICING ASSUMPTIONS, AND THE ABILITY TO SELL OIL OR GAS
         PRODUCTION AFTER CLOSING), (d) THE ENVIRONMENTAL CONDITION AND OTHER
         CONDITION OF THE ASSETS AND ANY POTENTIAL LIABILITY ARISING FROM OR
         RELATED TO THE ASSETS, AND (e) THE FAILURE OF ANY COMPUTER,
         ELECTRONICS, SOFTWARE, OR COMPONENTS TO BE FREE OF ANY BUGS OR ERRORS,
         INCLUDING, BUT NOT LIMITED TO, ANY DEFICIENCIES RELATING TO THE
         INABILITY TO PROPERLY FUNCTION BEYOND DECEMBER 31, 1999.

6.6      GAS ENTITLEMENTS AND IMBALANCES: To Unocal's Knowledge, except as
         described in Schedule 6.6 or in any other part of this Agreement,
         Unocal is not obligated by virtue of any prepayment made under any
         production sales contract or any other contract containing a
         take-or-pay clause, or under any similar arrangement, to deliver oil,
         gas or other minerals produced from or allocated to any of the Assets
         at any time after the Effective Date without receiving payment
         therefor.

6.7      NO BREACH: To Unocal's Knowledge, except as otherwise disclosed in
         this Agreement, Unocal is not party to, or subject to, or bound by any
         provision of any judgment, order, writ, injunction or decree of any
         court, or governmental body, or any statute, rule or regulation
         applicable to Unocal which prohibits or would be violated by, or which
         allows for the termination or modification of this Agreement due to
         Unocal entering into, executing, delivering or consummating same.

6.8      ENVIRONMENTAL CONDITION OF ASSETS: To Unocal's Knowledge, all material
         environmental problems affecting the Assets are referred to in
         documents which have been, or prior to Closing, will be provided or
         made available to Buyer, or are otherwise referred to in the Unocal
         Disclosure Schedule or described in Schedule 6.8 ("Environmental
         Disclosure Schedule"). Unocal and TBI acknowledge that (i) there are
         certain environmental conditions referenced on Schedule 6.8 which have
         not yet become specific and identifiable third party claims and that
         the inclusion of such conditions shall not preclude claims which arise
         after the Closing Date from being categorized as and treated hereunder
         as Qualified Claims even


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         though such claims relate to such generally described environmental
         conditions (to the extent that such claims otherwise meet the criteria
         of Qualified Claims, as defined herein), and (ii) that the
         environmental matters described on Schedule 6.8 which constitute
         specific and identifiable third party claims shall be the
         responsibility of TBI and shall not be eligible to become Qualified
         Claims after the Closing.

6.9      COMPLIANCE WITH LAWS AND AGREEMENTS: To Unocal's Knowledge, Unocal is
         in compliance with all permits, contracts and agreements relating to
         the Assets, and in compliance with all laws, rules and regulations of
         federal, state or local entities which have jurisdiction over Unocal
         or the Assets such that any failure of compliance will not have an
         adverse effect on the value of the Assets.

6.10     TAXES: To Unocal's Knowledge, all ad valorem, property, production,
         severance and similar taxes and assessments based on or measured by
         the ownership of property or the production or removal of Hydrocarbons
         or the receipt of proceeds therefrom and relating to the Assets, to
         the extent such taxes and assessments have become due and payable,
         have been timely paid and all applicable tax returns required to be
         filed have been filed and there are no claims by any applicable taxing
         authority pending against Unocal applicable to the Assets.

6.11     NO DISTRIBUTION: Unocal is acquiring the Shares for its own account
         for investment purposes and not with a view to or for sale in
         connection with any distributions thereof within the meaning of the
         Securities Act of 1933, as amended (the "Securities Act"), and the
         rules and regulations thereunder and any applicable state securities
         laws. Unocal understands that the Common Stock will not have been
         registered pursuant to the Securities Act or any applicable state
         securities or Blue Sky law, that such securities will be characterized
         as "restricted securities" under the federal securities laws and that
         under such laws and applicable regulations such securities cannot be
         sold or otherwise disposed of without registration under the
         Securities Act or an exemption therefrom. In this connection, Unocal
         represents that it is familiar with Rule 144, as currently in effect,
         and understands the resale limitations imposed thereby and by the
         Securities Act.

6.12     CURRENT COMMITMENTS: To Unocal's Knowledge, Schedule 6.12 contains a
         true and complete list as of the date of this Agreement of all
         authorities for expenditures ("AFEs") to drill or rework Wells, or for
         other capital expenditures, involving amounts in excess of $250,000
         pursuant to any of the contracts being assumed by Buyer for which all
         of the activities anticipated in such AFEs or commitments have not
         been completed by the date of this Agreement.

6.13     BROKERS: Unocal has not incurred any obligation or liability,
         contingent or otherwise, for any fee payable to a broker or finder
         with respect to the matters provided for in this Agreement which could
         be attributable to or charged to Buyer.


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6.14     OWNERSHIP OF COMMON STOCK: As of the date of this Agreement, neither
         Unocal nor its Affiliates own shares of Common Stock or other
         securities convertible into shares of Common Stock and are not a party
         to any agreements to acquire any such securities other than this
         Agreement.

6.15     ROYALTIES: To Unocal's knowledge, except as set forth in Exhibit "D,"
         all royalties and similar assessments based on or measured by the
         ownership of property or the production or removal of Hydrocarbons or
         the receipt of proceeds therefrom and relating to the Assets, to the
         extent such royalties have become due and payable, have been timely
         paid; provided, however, that notwithstanding anything to the
         contrary, Unocal does not make, and expressly disclaims, any
         representations or warranties regarding the manner or method of
         calculation of any such royalties.

                                   SECTION 7

                    REPRESENTATIONS AND WARRANTIES OF BUYER

         TBI hereby represents and warrants to Unocal as follows:

7.1      ORGANIZATION:

         (i)      Buyer is a corporation duly organized, validly existing and
                  in good standing under the laws of the state of Delaware, and
                  is qualified to do business and is in good standing as a
                  foreign corporation in every other jurisdiction where the
                  failure to so qualify would have a Party Adverse Effect on
                  Buyer.

         (ii)     Buyer has all requisite power and authority to own, lease or
                  operate its properties, assets and to carry on its business
                  as now conducted. Buyer is authorized to do business in the
                  states of Colorado, Wyoming, North Dakota and Utah.

         (iii)    Prior to the date of this Agreement, Buyer has delivered to
                  Unocal true, correct and complete copies of Buyer's
                  Certificate of Incorporation and Bylaws, as currently in
                  effect.

         (iv)     The respective headquarters and principal offices of Buyer
                  are located in the State of Texas.

7.2      AUTHORITY; ENFORCEABILITY:

         (i)      Buyer has all requisite corporate power and authority to
                  enter into and perform its obligations under this Agreement
                  and to carry out the transactions contemplated hereby.


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<PAGE>   40


         (ii)     All corporate acts and other proceedings required to be taken
                  by Buyer to authorize the execution, delivery and performance
                  by Buyer of this Agreement have been duly and properly taken.

         (iii)    This Agreement has been duly executed and delivered by Buyer
                  and constitutes the legal, valid and binding obligation of
                  Buyer, enforceable against Buyer in accordance with its
                  terms.

         (iv)     The execution, delivery and performance of this Agreement by
                  Buyer do not and will not conflict with, or result in any
                  violation of or default under any provision of the
                  Certificate of Incorporation or Bylaws of Buyer, or any law,
                  ordinance, rule, regulation, judgment, order, decree,
                  agreement, instrument or license applicable to Buyer or to
                  its properties or assets.

7.3      CONSENTS: Other than compliance with the Hart-Scott-Rodino Act,
         approval of the Buyer's board of directors, approval by Buyer's
         principal lenders and satisfaction of the covenants and conditions of
         this Agreement, no consent, approval, authorization, notice, filing,
         registration or qualification is required to be obtained or effected
         by Buyer for the execution, delivery or performance by Buyer of this
         Agreement.

7.4      LITIGATION, SUITS OR CLAIMS: To Buyer's Knowledge and except as
         reflected in Buyer's SEC Filings, there are no actions, suits or
         proceedings pending or threatened in writing against Buyer which if
         decided unfavorably to Buyer could have a Party Adverse Effect on
         Buyer.

7.5      NO BREACH: To Buyer's Knowledge, Buyer is not party to, or subject to,
         or bound by any provision of any judgment, order, writ, injunction or
         decree of any court, or governmental body, or any statute, rule or
         regulation applicable to Buyer which prohibits or would be violated
         by, or which allows for the termination or modification of this
         Agreement due to Buyer entering into, executing, delivering or
         consummating same.

7.6      COMPLIANCE WITH LAWS AND AGREEMENTS: To Buyer's Knowledge, Buyer is in
         substantial compliance with all Permits, contracts and agreements
         relating to its properties, assets and business and in substantial
         compliance with all laws, rules and regulations of federal, state or
         local entities which have jurisdiction over Buyer or its properties,
         assets or business such that any failure of compliance will not have a
         Party Adverse Effect on Buyer.

7.7      INVESTIGATIONS OF ASSETS: In accordance with the provisions of this
         Agreement, Buyer has made, or will make or arrange for others to make,
         such inspection of the Assets as it deems


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<PAGE>   41


         appropriate, and, except as otherwise provided herein, Buyer will
         accept the Assets "AS IS," "WHERE IS" AND "WITH ALL FAULTS AS TO ALL
         MATTERS."

7.8      NO DISTRIBUTION: Buyer is acquiring the Assets for its own account for
         investment purposes and not with a view to or for sale in connection
         with any distribution thereof within the meaning of the Securities Act
         of 1933, as amended, and the rules and regulations thereunder and any
         applicable state securities laws.

7.9      FEDERAL LEASES: If the Assets include any federal leases, Buyer is
         qualified to own such federal leases or will be so qualified at
         Closing.

7.10     CAPITALIZATION OF BUYER; TITLE TO THE SHARES: (a) The authorized
         capital stock of Buyer consists of (i) 55,000,000 shares of common
         stock, par value $0.10 per share, of which 29,259,989 shares are
         issued and outstanding and (ii) 2,500,000 shares of preferred stock,
         par value $0.10 per share, of which 1,000,000 shares are issued and
         outstanding; provided that the number of issued and outstanding shares
         of common stock is subject to increase pursuant to the exercise of
         previously granted options in the ordinary course. Except for this
         Agreement, or as otherwise disclosed in writing to Unocal by Buyer,
         and as set forth in the Buyer's SEC Filings, there are no outstanding
         options, warrants, agreements, conversion rights, preemptive rights or
         other rights to subscribe for, purchase or otherwise acquire any of
         the unissued or treasury shares of capital stock of Buyer.

         (b) Upon issuance and delivery to Unocal, the Shares shall be duly
         authorized, validly issued and fully paid and nonassessable, and no
         personal liability shall attach to the ownership thereof. Upon
         transfer of the Shares, from TBI at the Closing, Unocal will have
         valid and marketable title to all the Shares, free and clear of any
         Liens, other than any Liens arising by, through or under Unocal and
         the Stock Ownership and Registration Rights Agreement.

7.11     SEC FILINGS: (a) Buyer has filed with the Securities and Exchange
         Commission ("SEC"), and has heretofore made available to Unocal true
         and complete copies of, each form, registration statement, report,
         schedule, proxy or information statement and other document
         (including, without limitation, exhibits and amendments thereto),
         including, without limitation, its Annual Reports to stockholders
         incorporated by reference in certain of such reports, required to be
         filed by it or its predecessors with the SEC since January 1, 1998,
         under the Securities Exchange Act of 1934 (the "Exchange Act") or the
         Securities Act (collectively, the "SEC Filings").

         (b) As of its respective filing date (or, if any SEC Filing was
         amended, as of the date such amendment was filed), each SEC Filing,
         including, without limitation, any financial


                                       33

<PAGE>   42


         statements or schedules included therein, complied as to form in all
         material respects with the applicable requirements of the Securities
         Act and the Exchange Act.

         (c) As of its filing date (or, if any SEC Filing was amended, as of
         the date such amendment was filed), each SEC Filing filed pursuant to
         the Exchange Act did not contain any untrue statement of a material
         fact or omit to state any material fact necessary in order to make the
         statements made therein, in the light of the circumstances under which
         they were made, not misleading.

         (d) Each such registration statement, as amended or supplemented, if
         applicable, filed by TBI pursuant to the Securities Act and
         constituting a SEC Filing did not, as of the date such statement or
         amendment became effective, contain any untrue statement of a material
         fact or omit to state any material fact required to be stated therein
         or necessary to make the statements therein not misleading.

         (e) There are no liabilities of TBI or any of its subsidiaries of any
         kind whatsoever, whether accrued, contingent, absolute, determined,
         determinable or otherwise, and there is no existing condition,
         situation or set of circumstances which could reasonably be expected
         to result in such a liability, other than: (i) liabilities or
         obligations disclosed in the SEC Filings made prior to the date hereof
         or provided for in the TBI Balance Sheet or disclosed in the notes
         thereto; (ii) liabilities or obligations which would not, individually
         or in the aggregate, have a Party Adverse Effect on TBI; and (iii)
         liabilities or obligations under this Agreement.

7.12     FINANCIAL STATEMENTS: The audited consolidated financial statements
         and unaudited consolidated interim financial statements of TBI
         included in the SEC Filings fairly present, in conformity with
         generally accepted accounting practices applied on a consistent basis
         (except as may be indicated in the notes thereto), the consolidated
         financial position of TBI and its subsidiaries as of the dates thereof
         and their consolidated results of operations and cash flows for the
         periods then ended (subject to normal year-end adjustments and the
         absence of financial footnotes in the case of any unaudited interim
         financial statements).

7.13     ABSENCE OF CERTAIN CHANGES: Except as disclosed in the SEC Filings
         made prior to the date hereof or as contemplated by this Agreement or
         with respect to any of the actions referred to in any of clauses (b)
         through (g) below to which Unocal has given its consent, since the TBI
         Balance Sheet Date, the business of TBI and its subsidiaries has been
         conducted in all material respects in the ordinary course consistent
         with past practices and there has not been:

         a)       any event, occurrence, development or set of circumstances or
                  facts which has had, individually or in the aggregate, a
                  Party Adverse Effect on TBI;



                                       34

<PAGE>   43





         b)       any declaration, setting aside or payment of any dividend