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                                                                     EXHIBIT 4.2


                           TRIBO PETROLEUM CORPORATION
                        TRI-UNION DEVELOPMENT CORPORATION
                           TRI-UNION OPERATING COMPANY

                                  130,000 UNITS
                                  CONSISTING OF

         $1,000 PRINCIPAL AMOUNT OF 12.5% SENIOR SECURED NOTES DUE 2006
                      OF TRI-UNION DEVELOPMENT CORPORATION

                                      WITH

                        ONE SHARE OF CLASS A Common Stock
                         OF TRIBO PETROLEUM CORPORATION

                               PURCHASE AGREEMENT

                                                                   June 13, 2001

JEFFERIES & COMPANY INC.
909 Fannin, Suite 3100
Houston, TX 77010

Ladies and Gentlemen:

         Tri-Union Development Corporation, a Texas corporation (the "Company"
or the "Issuer"), Tri-Union Operating Company, a Delaware corporation and a
wholly owned subsidiary of the Company (the "Subsidiary"), and Tribo Petroleum
Corporation, a Texas corporation and the parent corporation of the Issuer
("Tribo", and together with the Subsidiary, the "Guarantors"), hereby confirm
their agreement with you (the "Initial Purchaser") as set forth below.

         1. The Securities. Subject to the terms and conditions herein
contained, the Issuer and Tribo propose to issue and sell to the Initial
Purchaser an aggregate of 130,000 units (each a "Unit" and collectively, the
"Units"), each Unit consisting of $1,000 principal amount of 12.5% Series A
Senior Secured Notes due 2006 of the Issuer (the "Notes") and one share of
Tribo's Class A Common Stock, par value $.01 per share, of Tribo (the "Class A
Common Stock"). The Notes will initially be guaranteed (the "Guarantees") on a
senior secured basis by the Guarantors pursuant to a Guaranty Agreement, dated
as of the Closing Date, among the Company, the Guarantors and the other parties
thereto (the "Guaranty Agreement"). The Notes are to be issued under an
indenture (the "Indenture") to be dated as of June 18, 2001 by and among the
Issuer, Tribo and Firstar Bank, National Association (the "Trustee").
Additionally, the Initial Purchaser shall receive an aggregate of 65,000 shares
of Class B Common Stock, par value $.01 per share, of Tribo (the "Class B Common
Stock," and together with the Class A Common Stock, the


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"Common Stock"). The Notes, the Units, the Guarantees and the Common Stock are
collectively referred to herein as the "Securities." Pursuant to the Mortgage,
Deed of Trust, Assignment of Production, Security Agreement and Financing
Statement, dated as of the Closing Date, given by each of the Issuer and the
Subsidiary (the "Mortgages"), the Issuer and the Subsidiary will grant and
pledge to Wells Fargo Bank Minnesota, National Association, as collateral agent
(the "Collateral Agent"), for the equal and ratable benefit of the holders of
the Notes (the "Noteholders") and certain other parties described therein, a
security interest in substantially all of the crude oil and natural gas
properties of the Company and the Subsidiary. The Mortgages, together with (i)
the Guaranty Agreement, (ii) the Pledge and Collateral Account Agreement, dated
as of the Closing Date, among the Company, the Collateral Agent and the other
parties thereto (the "Pledge Agreement"), and (iii) the Intercreditor and
Collateral Agency Agreement, dated as of the Closing Date, among the Company,
the Guarantors, the Trustee, the Collateral Agent and the other parties thereto,
are sometimes referred to herein collectively as the "Security Documents."

         The Securities will be offered and sold to the Initial Purchaser
without being registered under the Securities Act of 1933, as amended (the
"Act"), in reliance on exemptions therefrom. The Notes will be issued pursuant
to the Issuer's First Amended Plan of Reorganization (the "Plan") and an order
(the "Confirmation Order") entered by The United States Bankruptcy Court for the
Southern District of Texas, Houston Division (the "Bankruptcy Court") in In re
Tri-Union Development Corporation (Case No. 00-32498-H4-11) (the "Bankruptcy
Case"), on May 23, 2001 (the "Confirmation Date") in accordance with 11 U.S.C.
Section 1129.

         In connection with the sale of the Securities, the Issuer and the
Guarantors have prepared a final offering memorandum dated June 13, 2001 (the
"Final Memorandum" or "Memorandum"), setting forth or including, among other
things, a description of the terms of the Securities, the terms of the offering
of the Securities and a description of the business and assets of the Issuer and
the Guarantors and any material developments relating to the Issuer and the
Guarantors occurring after the date of the most recent historical financial
statements included therein.

         The Initial Purchaser and its direct and indirect transferees of the
Units (and the related Guarantees) will be entitled to the benefits of a
registration rights agreement to be dated as of the Closing Date (as defined in
Section 3 below) (the "Notes Registration Rights Agreement"), pursuant to which
the Issuer and the Guarantors will agree, among other things, to file with the
Securities and Exchange Commission (the "Commission"), under the circumstances
set forth therein, (i) a registration statement under the Act (the "Exchange
Offer Registration Statement"), relating to Series B Senior Secured Notes due
2006 of the Issuer (the "Exchange Notes") to be offered in exchange (the
"Exchange Offer") for the Notes, and (ii) as and to the extent required by the
Notes Registration Rights Agreement, a shelf registration statement pursuant to
Rule 415 under the Act (the "Notes Shelf Registration Statement"), relating to
the resale by certain holders of the Notes. The Initial Purchaser and its direct
and indirect transferees will also be entitled to the benefits of an additional
registration rights agreement, dated as of the Closing Date (the "Equity
Registration Rights Agreement"), pursuant to which the Noteholders and the
Initial Purchaser will be entitled to, among other things, the registration
under the Act of their shares of Common Stock pursuant to a registration
statement to be filed by Tribo (the "Equity Registration Statement," and,
together with the Exchange Offer Registration Statement and the Notes Shelf


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Registration Statement, the "Registration Statements") and to use their best
efforts to cause such Registration Statements to be declared effective. This
Purchase Agreement (this "Agreement"), the Securities, the Indenture, the Notes
Registration Rights Agreement, the Equity Registration Rights Agreement, and the
Security Documents are hereinafter referred to collectively as the "Operative
Documents."

         2. Representations and Warranties. The Issuer and the Guarantors,
jointly and severally, represent and warrant to the Initial Purchaser that:

                  (a) Neither the Final Memorandum nor any amendment or
         supplement thereto as of the date thereof and at all times subsequent
         thereto up to the Closing Date contained or contains any untrue
         statement of a material fact or omitted or omits to state a material
         fact necessary to make the statements therein, in the light of the
         circumstances under which they were made, not misleading, except that
         the representations and warranties set forth in this Section 2(a) do
         not apply to statements or omissions made in reliance upon and in
         conformity with information relating to the Initial Purchaser furnished
         to the Issuer or the Guarantors in writing by the Initial Purchaser
         expressly for use in the Final Memorandum or any amendment or
         supplement thereto.

                  (b) Tribo has the authorized, issued and outstanding
         capitalization as set forth in the Final Memorandum; all of the
         outstanding shares of capital stock of the Issuer and of each of the
         Guarantors have been, and as of the Closing Date will be, duly
         authorized and validly issued, are fully paid and nonassessable and
         were not issued in violation of any preemptive or similar rights; all
         of the outstanding shares of capital stock of the Subsidiary are and,
         as of the Closing Date, will be, owned by the Company free and clear of
         all liens, encumbrances, equities and claims or restrictions on
         transferability (other than those imposed by the Act and the securities
         or "Blue Sky" laws of certain jurisdictions) or voting; all of the
         outstanding shares of capital stock of the Company are and, as of the
         Closing Date, will be, owned by Tribo free and clear of all liens,
         encumbrances, equities and claims or restrictions on transferability
         (other than those imposed by the Act and the securities or "Blue Sky"
         laws of certain jurisdictions) or voting; except as set forth in the
         Final Memorandum, there are no outstanding (i) options, warrants or
         other rights to purchase, (ii) agreements or other obligations of the
         Issuer or the Guarantor to issue or (iii) other rights to convert any
         obligation into, or exchange any securities for, shares of capital
         stock of or ownership interests in the Issuer or the Guarantors. Except
         as disclosed in the Final Memorandum, neither the Issuer nor any of the
         Guarantors owns, directly or indirectly, any shares of capital stock or
         any other equity or long-term debt securities or have any equity
         interest in any firm, partnership, joint venture or other entity.

                  (c) The Issuer and each of the Guarantors is duly
         incorporated, validly existing and in good standing under the laws of
         its respective jurisdiction of incorporation and has all requisite
         corporate power and authority to own its properties and conduct its
         business as now conducted and as described in the Final Memorandum; the
         Issuer and each of the Guarantors is duly qualified to do business as a
         foreign corporation in good standing in all other jurisdictions where
         the ownership or leasing of its properties or the conduct of its
         business requires such qualification, except where the failure to be so


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         qualified would not, individually or in the aggregate, have a material
         adverse effect on the general affairs, management, business, assets,
         condition (financial or otherwise) or results of operations of the
         Issuer and the Guarantors considered as a whole (any such event, a
         "Material Adverse Effect").

                  (d) The Issuer and each of the Guarantors has all requisite
         corporate power and authority to execute, deliver and perform its
         respective obligations under this Agreement and the other Operative
         Documents to which it is a party and to consummate the transactions
         contemplated hereby and thereby, including, without limitation, the
         power and authority to issue, sell and deliver the Securities as
         contemplated by this Agreement.

                  (e) This Agreement has been duly and validly authorized,
         executed and delivered by the Issuer and each of the Guarantors.

                  (f) The Indenture and each other Operative Document to which
         the Issuer or any of the Guarantors is a party has been duly and
         validly authorized by the Issuer and the Guarantors (to the extent a
         party thereto) and, when duly executed and delivered (assuming the due
         authorization, execution and delivery thereof by each other party
         thereto), will be the valid and legally binding agreement of the Issuer
         and the Guarantors, enforceable against each of them in accordance with
         its terms, except as such enforceability may be limited by bankruptcy,
         insolvency, reorganization, moratorium and other similar laws now or
         hereinafter in effect relating to or affecting creditors' rights
         generally and to general principles of equity (regardless of whether
         such enforceability is considered in a proceeding in equity or at law).
         The Indenture meets the requirements for qualification under the Trust
         Indenture Act of 1939, as amended (the "TIA").

                  (g) The Notes have been duly and validly authorized for
         issuance and sale to the Initial Purchaser by the Issuer pursuant to
         this Agreement and, when issued and authenticated in accordance with
         the terms of the Indenture and delivered against payment therefor in
         accordance with the terms hereof, will be the legally valid and binding
         obligations of the Issuer, enforceable against it in accordance with
         their terms and entitled to the benefits of the Indenture, except as
         such enforceability may be limited by bankruptcy, insolvency,
         reorganization, moratorium and other similar laws now or hereinafter in
         effect relating to or affecting creditors' rights generally and to
         general principles of equity (regardless of whether such enforceability
         is considered in a proceeding in equity or at law).

                  (h) The Exchange Notes have been duly and validly authorized
         for issuance by the Issuer and, when issued and authenticated in
         accordance with the terms of the Indenture, the Notes Registration
         Rights Agreement and the Exchange Offer, will be the legally valid and
         binding obligations of the Issuer, enforceable against it in accordance
         with their terms and entitled to the benefits of the Indenture, except
         as such enforceability may be limited by bankruptcy, insolvency,
         reorganization, moratorium and other similar laws now or hereinafter in
         effect relating to or affecting creditors' rights generally and to
         general principles of equity (regardless of whether such enforceability
         is considered in a proceeding in equity or at law).


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                  (i) Each of the Notes Registration Rights Agreement and the
         Equity Registration Rights Agreement have been duly authorized by the
         Issuer, the Subsidiary and Tribo, as applicable, and, when duly
         executed and delivered by the Issuer, the Subsidiary and Tribo, as
         applicable (assuming the due execution and delivery thereof by the
         Initial Purchaser), will be the legally valid and binding obligation of
         the Issuer, the Subsidiary and Tribo, as applicable, enforceable
         against each of them in accordance with its terms, except as such
         enforceability may be limited by bankruptcy, insolvency,
         reorganization, moratorium and other similar laws now or hereinafter in
         effect relating to or affecting creditors' rights generally and to
         general principles of equity (regardless of whether such enforceability
         is considered in a proceeding in equity or at law) and, as to rights of
         indemnification and contribution, by principles of public policy or
         U.S. federal or state securities laws relating thereto.

                  (j) The shares of Class A Common Stock and Class B Common
         Stock to be issued to the Noteholders and the Initial Purchaser,
         respectively, have been duly and validly authorized for issuance by
         Tribo and, when issued, will be duly authorized, validly issued, fully
         paid and non-assessable and will not be subject to any preemptive or
         similar rights.

                  (k) After giving effect to the Plan and the Confirmation
         Order, no consent, waiver, approval, authorization or order of or
         filing, registration, qualification, license or permit of or with any
         court or governmental agency or body, or third party is required for
         (i) the issuance and sale by the Issuer of the Notes to the Initial
         Purchaser or the consummation by the Issuer of each of the other
         transactions contemplated hereby or by any of the other Operative
         Documents, (ii) the issuance and sale by the Guarantors of the
         Guarantees or the consummation by the Guarantors of the other
         transactions contemplated hereby or by any of the Operative Documents,
         or (iii) the issuance and sale by Tribo of the Common Stock, except, in
         each case, such as have been or, prior to the Closing Date, will be
         obtained, and other than such as may be required under state securities
         or "Blue Sky" laws in connection with the purchase and resale of the
         Securities by the Initial Purchaser and the receipt by the Issuer and
         the Guarantors of an order from the Commission declaring the Exchange
         Offer Registration Statement, the Shelf Registration Statement and/or
         the Equity Registration Statement effective. Neither the Issuer nor any
         of the Guarantors is (i) in violation of its charter or bylaws, (ii)
         after giving effect to the Plan and the Confirmation Order, in breach
         or violation of any statute, judgment, decree, order, rule or
         regulation applicable to any of them or any of their respective
         properties or assets, except for any such breach or violation which
         would not, individually or in the aggregate, have a Material Adverse
         Effect, or (iii) after giving effect to the Plan and the Confirmation
         Order, in breach of or default under (nor has any event occurred which,
         with notice or passage of time or both, would constitute a default
         under) or in violation of any of the terms or provisions of any
         indenture, mortgage, deed of trust, loan agreement, note, lease,
         license, permit, certificate, contract or other agreement or instrument
         to which any of them is a party or to which any of them or their
         respective properties or assets is subject (collectively, "Contracts"),
         except for any such breach, default, violation or event which would
         not, individually or in the aggregate, have a Material Adverse Effect.


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                  (l) As of the Closing Date, the execution, delivery and
         performance by the Issuer and the Guarantors of this Agreement and each
         of the other Operative Documents (to the extent a party thereto) and
         the consummation of the transactions contemplated hereby and thereby
         (including, without limitation, the issuance and sale of the Securities
         to the Initial Purchaser and the issuance of the Exchange Notes in the
         Exchange Offer), do not and will not violate, conflict with or
         constitute or result in a breach of or a default under (or constitute
         an event which with notice or passage of time or both would constitute
         a default under) or cause an acceleration of any obligation under, or
         (except for the transactions contemplated hereby and thereby) result in
         the imposition or creation of (or the obligation to create or impose)
         any lien, security interest or encumbrance on any properties or assets
         of either the Issuer or any Guarantor with respect to (i) the terms or
         provisions of any Contract, except for any such conflict, breach,
         violation, default or event which would not, individually or in the
         aggregate, have a Material Adverse Effect, (ii) the charter or bylaws
         (or similar organizational document) of the Issuer or any of the
         Guarantors, or (iii) (assuming compliance with all applicable state
         securities or "Blue Sky" laws and assuming the accuracy of the
         representations and warranties of the Initial Purchaser in Section 8
         hereof) any statute, judgment, decree, order, rule or regulation
         applicable to the Issuer or any of the Guarantors or any of their
         respective properties or assets.

                  (m) Each of BDO Seidman, LLP and Hidalgo, Banfill, Zlotnik &
         Kermali, P.C., who are reporting on the audited financial statements of
         the Issuer included in the Final Memorandum, are, with respect to the
         Issuer and each of the Guarantors, independent public accountants
         within the meaning of the Act and the rules and regulations promulgated
         thereunder. The audited financial statements of Tribo and related notes
         thereto included in the Final Memorandum present fairly in all material
         respects the consolidated financial position of the Issuer and the
         Guarantors, as of the dates indicated and the consolidated results of
         their operations and cash flow for the periods specified, and are in
         accordance in all material respects with the applicable requirements of
         Regulation S-X promulgated under the Securities Exchange Act of 1934,
         as amended (the "Exchange Act"), as though such audited financial
         statements were being presented in a registration statement on Form S-1
         under the Act. The summary and selected financial and statistical data
         included in the Final Memorandum present fairly in all material
         respects the information shown therein and have been prepared and
         compiled on a basis consistent with the audited financial statements
         included therein.

                  (n) The pro forma financial statements (including the notes
         thereto) and the other pro forma financial information included in the
         Final Memorandum (i) comply as to form in all material respects with
         the applicable requirements of Regulation S-X promulgated under the
         Exchange Act, (ii) have been prepared in all material respects in
         accordance with the Commission's rules and guidelines with respect to
         pro forma financial statements, and (iii) have been properly computed
         on the bases described therein; in each case as though such pro forma
         financial statements were being presented in a registration statement
         on Form S-1 under the Act, the assumptions used in the preparation of
         the pro forma financial data and other pro forma financial information
         included in the Final Memorandum are reasonable and the adjustments
         used therein are appropriate to give effect to the transactions or
         circumstances referred to therein.


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                  (o) The historical information underlying the estimates of the
         reserves of the Company and the Guarantors supplied by the Company and
         the Guarantors to Huddleston & Co., Inc. and DeGolyer and MacNaughton,
         independent petroleum and geological engineering firms (the "Petroleum
         Engineers"), for the purposes of preparing the reserve reports of the
         Company referenced in the Final Memorandum (the "Reserve Reports"),
         including, without limitation, production volumes, sales prices for
         production, contractual pricing provisions under oil or gas sales or
         marketing contracts or under hedging arrangements, costs of operations
         and development, and working interest and net revenue information
         relating to the Company's and the Guarantors' ownership interests in
         properties, was true and correct in all material respects on the date
         of such Reserve Reports; the estimates of future capital expenditures
         and other future exploration and development costs supplied to the
         Petroleum Engineers were prepared in good faith and with a reasonable
         basis; the information provided to the Petroleum Engineers for purposes
         of preparing the Reserve Reports was prepared in accordance with
         customary industry practices; to the best of the Company's knowledge,
         the Petroleum Engineers were, as of the date of the Reserve Reports
         prepared by them, and are, as of the date hereof, independent petroleum
         and geological engineers with respect to the Company; and other than
         normal production of reserves and intervening spot market product price
         fluctuations, and except as disclosed in the Final Memorandum, neither
         the Company nor any of the Guarantors is aware of any facts or
         circumstances that have the potential to have a Material Adverse Effect
         on the reserves in the aggregate, or the aggregate present value of
         future net cash flows therefrom, as described in the Final Memorandum
         and as reflected in the Reserve Reports.

                  (p) Except as described in the Final Memorandum, as of the
         date hereof, (i) except for royalties held in suspense by the Issuer in
         the ordinary course of business, all royalties, rentals, deposits and
         other amounts due on the oil and gas properties of the Company and the
         Guarantors have been properly and timely paid, and no proceeds from the
         sale or production attributable to the oil and gas properties of the
         Company and the Guarantors are currently being held in suspense by any
         purchaser thereof, except where such amounts due could not, singly or
         in the aggregate, have a Material Adverse Effect on the Company or the
         Guarantors, and (ii) there are no claims under take-or-pay contracts
         pursuant to which natural gas purchasers have any make-up rights
         affecting the interests of the Company or the Guarantors in their
         respective oil and gas properties, except where such claims could not,
         singly or in the aggregate, have a Material Adverse Effect on the
         Company or the Guarantors.

                  (q) The Bankruptcy Court has entered the Confirmation Order in
         the Bankruptcy Case, confirming the Plan on the Confirmation Date in
         accordance with 11 U.S.C. Section 1129. The Confirmation Order is a
         Final Order (as defined in the Plan) and the Plan is not subject and,
         as of the Closing Date, will not be subject to a stay or injunction
         issued by any court of competent jurisdiction. Neither the Plan nor the
         Confirmation Order have been modified, amended or revoked, and the Plan
         and Confirmation Order are in full force and effect.

                  (r) No order has been entered in the Bankruptcy Case
         converting such Bankruptcy Case to a case under Chapter 7 of the United
         States Bankruptcy Code,


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         appointing a trustee or examiner in the Bankruptcy Case pursuant to 11
         U.S.C. Section 1104, dismissing the Bankruptcy Case or granting relief
         from the automatic stay of 11 U.S.C. Section 362 to allow any person or
         entity to enforce any lien or security interest in any portion of the
         Issuer's assets or properties.

                  (s) Except as disclosed in the Final Memorandum, there is not
         pending or, to the knowledge of the Issuer or the Guarantors,
         threatened any action, suit, proceeding, inquiry or investigation to
         which the Issuer or any of the Guarantors is a party, or to which the
         property or assets of the Issuer or any of the Guarantors is subject,
         before or brought by any court, arbitrator or governmental agency or
         body which, if determined adversely to the Issuer or any of the
         Guarantors, would, individually or in the aggregate, have a Material
         Adverse Effect or which seeks to restrain, enjoin, prevent the
         consummation of or otherwise challenge the issuance or sale of the
         Securities to be sold hereunder or the consummation of the other
         transactions described in the Final Memorandum.

                  (t) Each of the Issuer and the Guarantors possesses all
         licenses, permits, certificates, consents, orders, approvals and other
         authorizations from, and has made all declarations and filings with,
         all federal, state, local and other governmental authorities, all
         self-regulatory organizations and all courts and other tribunals,
         presently required or necessary to own or lease, as the case may be,
         and to operate its respective properties and to carry on its respective
         businesses as now or proposed to be conducted as set forth in the Final
         Memorandum ("Permits"), except where the failure to obtain such Permits
         would not, individually or in the aggregate, have a Material Adverse
         Effect; each of the Issuer and the Guarantors has fulfilled and
         performed all of its obligations with respect to such Permits and no
         event has occurred which allows, or after notice or lapse of time would
         allow, revocation or termination thereof or results in any other
         material impairment of the rights of the holder of any such Permit,
         except where the failure to perform such obligations or the occurrence
         of such event would not have a Material Adverse Effect; and neither the
         Issuer nor any of the Guarantors has received any notice of any
         proceeding relating to revocation or modification of any such Permit,
         except as described in the Final Memorandum and except where such
         revocation or modification would not, individually or in the aggregate,
         have a Material Adverse Effect.

                  (u) Since the respective dates as of which information is
         given in the Final Memorandum, except as described therein and except
         for the transactions contemplated in the Operative Documents, (i)
         neither the Issuer nor any of the Guarantors has incurred any
         liabilities or obligations (whether liquidated, unliquidated, fixed,
         contingent, matured, unmatured, disputed, undisputed, legal, equitable,
         secured or unsecured), or entered into or agreed to enter into any
         transactions or contracts (whether written or oral) not in the ordinary
         course of business, (ii) the Issuer and each Guarantor has timely paid
         all liabilities or obligations incurred in the ordinary course of its
         business consistent with past practices, (iii) neither the Issuer nor
         any of the Guarantors has purchased any of its outstanding capital
         stock, nor declared, paid or otherwise made any dividend or
         distribution of any kind on its capital stock and (iv) there has not
         been any change in the capital stock or long-term indebtedness of the
         Issuer or any of the Guarantors.


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                  (v) Each of the Issuer and the Guarantors has filed all
         necessary federal, state and foreign income and franchise tax returns,
         except where the failure to so file such returns would not,
         individually or in the aggregate, have a Material Adverse Effect, and
         has paid all taxes shown as due thereon except as to taxes any of the
         Issuer or Guarantors is contesting in good faith; and other than tax
         deficiencies which the Issuer or Guarantors is contesting in good faith
         and for which such Issuer or such Guarantors has provided adequate
         reserves in accordance with generally accepted accounting principles,
         there is no tax deficiency that has been asserted against the Issuer or
         the Guarantors that would have, individually or in the aggregate, a
         Material Adverse Effect.

                  (w) The statistical and market-related data included in the
         Final Memorandum are based on or derived from sources which the Issuer
         believes to be reliable and accurate.

                  (x) Neither the Issuer nor any of the Guarantors or any agent
         acting on their behalf has taken or will take any action that might
         cause this Agreement or the sale of the Securities to violate
         Regulation T, U or X of the Board of Governors of the Federal Reserve
         System, in each case as in effect, or as the same may hereafter be in
         effect, on the Closing Date.

                  (y) As of the Closing Date, each of the Issuer and the
         Guarantors has good and defensible title to all real property and good
         title to all personal property described in the Final Memorandum as
         being owned by it and good and defensible title to a leasehold estate
         in the real and personal property described in the Final Memorandum as
         being leased by it free and clear of all liens, security interests,
         charges, encumbrances or restrictions, except (i) as described in the
         Final Memorandum, or (ii) Permitted Liens (as defined in the Indenture)
         to the extent the failure to have such title or the existence of such
         liens, security interests, charges, encumbrances or restrictions would
         not, individually or in the aggregate, have a Material Adverse Effect.
         As of the Closing Date, all Contracts to which the Issuer or any
         Guarantor is a party or by which any of them is bound are valid and
         enforceable against the Issuer and each Guarantor, as the case may be,
         and, to the knowledge of the Issuer and each Guarantor, are valid and
         enforceable against the other party or parties thereto and are in full
         force and effect, except as such enforceability may be limited by
         bankruptcy, insolvency, reorganization, moratorium and other similar
         laws now or hereinafter in effect relating to or affecting creditors'
         rights generally, by general equitable principles (regardless of
         whether such enforceability is considered in a proceeding in equity or
         at law) or the discretion of the court before which any proceeding
         therefor may be brought.

                  (z) The Issuer and the Guarantors own or possess adequate
         licenses or other rights to use all patents, trademarks, service marks,
         trade names, copyrights and know-how necessary to conduct the
         businesses now or proposed to be operated by them as described in the
         Final Memorandum, and neither the Issuer nor any of the Guarantors has
         received any notice of infringement of or conflict with (or knows of
         any such infringement of or conflict with) asserted rights of others
         with respect to any patents, trademarks, service marks, trade names,
         copyrights or know-how which, if such assertion of infringement or
         conflict were sustained, would have a Material Adverse Effect.


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                  (aa) There are no legal or governmental proceedings involving
         or affecting the Issuer or any of the Guarantors or any of their
         respective properties or assets which would be required to be described
         in a prospectus pursuant to the Act that are not so described in the
         Final Memorandum, nor are there any material contracts or other
         documents which would be required to be described in a prospectus
         pursuant to the Act that are not so described in the Final Memorandum.

                  (bb) Except as disclosed in the Final Memorandum or as would
         not, individually or in the aggregate, have the potential to have a
         Material Adverse Effect (i) each of the Issuer and the Guarantors is in
         compliance with and not subject to any pending or, to the knowledge of
         the Issuer or any of the Guarantors, threatened liability under
         applicable Environmental Laws (as defined below), (ii) each of the
         Issuer and the Guarantors has made all filings and provided all notices
         required under any applicable Environmental Law, and has, and is in
         compliance with, all Permits required under any applicable
         Environmental Laws for the current operations and each of them is in
         full force and effect, (iii) there is no civil, criminal or
         administrative action, suit, demand, claim, hearing, notice of
         violation, investigation, proceeding, notice or demand letter or
         request for information pending or, to the knowledge of the Issuer and
         the Guarantors, threatened against the Issuer or the Guarantors under
         any Environmental Law, (iv) no lien, charge, encumbrance or restriction
         has been recorded under any Environmental Law with respect to any
         assets, facility or property owned, operated, leased or controlled by
         the Issuer or any of the Guarantors, (v) neither the Issuer nor any of
         the Guarantors has received notice that it has been identified as a
         potentially responsible party under the Comprehensive Environmental
         Response, Compensation and Liability Act of 1980, as amended
         ("CERCLA"), or any comparable state law, (vi) no property or facility
         of any of the Issuer or the Guarantors is (A) listed or, to the
         knowledge of the Issuer and the Guarantors proposed for listing on the
         National Priorities List under CERCLA or (B) listed in the
         Comprehensive Environmental Response, Compensation, Liability
         Information System List promulgated pursuant to CERCLA, or on any
         comparable list maintained by any United States federal, state,
         municipal, local, territorial or other governmental subdivision,
         department, commission, board, bureau, agency, regulatory authority,
         instrumentality or judicial or administrative body (each a
         "Governmental Authority"), and (vii) notwithstanding anything in this
         Section 2(bb) to the contrary, no facts or circumstances exist and no
         event or condition is occurring or, to any of Issuer's or Guarantors'
         knowledge, has occurred, with respect to Issuer or the Guarantors and
         relating to any Environmental Law, any release of any hazardous, toxic,
         dangerous, or petroleum hydrocarbon material, substance, or waste, any
         chemical, any solid waste, or any other pollutant or contaminant, or
         any of Issuer's or Guarantors' compliance with all current or
         reasonably foreseeable future requirements of Environmental Law, that
         individually or in the aggregate has the potential to have a Material
         Adverse Effect.

                  For purposes of this Agreement, "Environmental Laws" means the
         common law and all applicable federal, state and local laws,
         regulations, rules, ordinances, codes, orders, decrees, judgments,
         injunctions or any other legally enforceable requirement issued,
         promulgated, approved or entered thereunder, relating to pollution or
         protection of public or employee health and safety or the environment,
         including, without limitation, laws relating to (i) emissions,
         discharges, releases or threatened releases of hazardous


                                       10
<PAGE>   11


         materials into the environment (including, without limitation, ambient
         air, surface water, ground water, land surface or subsurface strata),
         (ii) the manufacture, processing, distribution, use, generation,
         treatment, storage, disposal, transport, arrangement for disposal or
         transport or handling of hazardous, toxic, dangerous, or petroleum
         hydrocarbon material, substance, or waste, any chemical, any solid
         waste, or any other pollutant or contaminant, and (iii) underground and
         above ground storage tanks and related piping, and emissions,
         discharges, releases or threatened releases therefrom.

                  (cc) There is no strike, labor dispute, slowdown or work
         stoppage with the employees of any of the Issuer or the Guarantors
         which is pending or, to the knowledge of the Issuer, threatened.

                  (dd) Each of the Issuer and the Guarantors carries insurance,
         including self-insurance, in such amounts and covering such risks as in
         its reasonable determination is adequate for the conduct of its
         business and the value of its properties.

                  (ee) Neither the Issuer nor any of the Guarantors has incurred
         any liability for any prohibited transaction or funding deficiency or
         any complete or partial withdrawal liability with respect to any
         pension, profit sharing or other plan which is subject to the Employee
         Retirement Income Security Act of 1974, as amended ("ERISA"), to which
         the Issuer or the Guarantors makes or ever has made a contribution and
         in which any employee of the Issuer or the Guarantors is or has ever
         been a participant, which in the aggregate could have a Material
         Adverse Effect. With respect to such plans, each of the Issuer and the
         Guarantors is in compliance in all respects with all applicable
         provisions of ERISA, except where the failure to so comply would not,
         individually or in the aggregate, have a Material Adverse Effect.

                  (ff) Each of the Issuer and the Guarantors (i) makes and keeps
         accurate books and records and (ii) maintains internal accounting
         controls which provide reasonable assurance that (A) transactions are
         executed in accordance with management's authorization, (B)
         transactions are recorded as necessary to permit preparation of its
         financial statements and to maintain accountability for its assets, (C)
         access to its assets is permitted only in accordance with management's
         authorization and (D) the reported accountability for its assets is
         compared with existing assets at reasonable intervals.

                  (gg) As of the Closing, after giving effect to the
         transactions contemplated hereby, neither the Issuer nor any of the
         Guarantors will be an "investment company" or "promoter" or "principal
         underwriter" for an "investment company," as such terms are defined in
         the Investment Company Act of 1940, as amended, and the rules and
         regulations thereunder.

                  (hh) The Units, the Notes, the Guarantees, the Class A Common
         Stock, the Class B Common Stock, the Indenture, and the Notes
         Registration Rights Agreement, the Equity Registration Rights Agreement
         and the Security Documents conform in all material respects to the
         descriptions thereof contained in the Final Memorandum.


                                       11
<PAGE>   12


                  (ii) The Final Memorandum, as of its date, contains all the
         information specified in, and meeting the requirements of, Rule
         144A(d)(4) under the Act.

                  (jj) No holder of securities of the Issuer or any Guarantor
         will be entitled to have such securities registered under the
         registration statements required to be filed by the Issuer or any
         Guarantor pursuant to either of the Registration Rights Agreement or
         the Equity Registration Rights Agreement, other than as expressly
         permitted thereby.

                  (kk) Credit Lyonnais, New York Branch, as agent for certain
         lenders ("Credit Lyonnais") party to that certain Amended and Restated
         Credit Agreement (as heretofore modified and amended, the "Credit
         Agreement") by and among the Issuer, Credit Lyonnais and said lenders,
         dated as of March 31, 1998, has delivered a letter (the "Payoff
         Letter") acknowledging, among other things, the payment in full on the
         Closing Date by the Issuer of the Obligations (as defined in the Credit
         Agreement) and the unconditional release by Credit Lyonnais of all
         Lender Liens (as defined in the Credit Agreement) under the Credit
         Agreement and all related Collateral Documents (as defined in the
         Credit Agreement). With respect to each of the claims and liabilities
         described on Exhibit A hereto (collectively, the "Lien Claims"), fully
         executed releases of such claims and liabilities and any and all liens
         and security interests securing the same, suitable for filing with the
         appropriate Governmental Authorities and otherwise satisfactory in form
         and substance to counsel for the Initial Purchaser, have been delivered
         to the Lien Agent. Upon receipt from the Issuer by the Lien Agent of
         the full amount of the Lien Claims, the Lien Agent is unconditionally
         obligated to release and deliver such releases for filing with the
         appropriate Governmental Authorities.

                  (ll) The total aggregate amount of the Issuer's and
         Guarantors' liability on the date hereof with respect to the disputed
         claims and liabilities is described on Exhibit B attached hereto
         (collectively, the "Disputed Claims"). To the best of the Issuer's and
         the Guarantors' knowledge, there are no facts or circumstances which
         (with the passage of time or the giving of notice or both) could give
         rise to any additional claims or liabilities against the Issuer or the
         Guarantors in connection with the Disputed Claims or increase the total
         aggregate amount of the Disputed Claims.

                  (mm) Immediately after the consummation of the transactions
         contemplated by this Agreement and the Indenture, (i) the fair value
         and present fair saleable value of the assets of each of the Issuer and
         the Guarantors will exceed the sum of its stated liabilities and
         identified contingent liabilities; neither the Issuer nor any of the
         Guarantors (each on a consolidated basis) is, nor will the Issuer or
         the Guarantors (each on a consolidated basis) be, after giving effect
         to the execution, delivery and performance of this Agreement and each
         of the other Operative Documents, and the consummation of the
         transactions contemplated hereby and thereby, (A) left with
         unreasonably small capital with which to carry on its business as it is
         proposed to be conducted, (B) unable to pay its debts (contingent or
         otherwise) as they mature or (C) otherwise insolvent, and (ii) the
         Issuer and each of the Guarantors will, upon the issuance of the Notes
         and the grant of the Mortgages, Guarantees and liens and security
         interests in connection therewith, receive a reasonably equivalent
         value or fair consideration for such indebtedness and the grant of
         security therefor, so that, in any event, the issuance of the Notes and
         the grant of security


                                       12
<PAGE>   13


         therefor will not constitute a fraudulent transfer or conveyance under
         any applicable federal or state law providing protection for creditors
         from and against a fraudulent transfer or conveyance.

                  (nn) Neither the Issuer nor any of the Guarantors or any of
         their respective Affiliates (as defined in Rule 501(b) of Regulation D
         under the Act) has directly, or through any agent, (i) sold, offered
         for sale, solicited offers to buy or otherwise negotiated in respect
         of, any "security" (as defined in the Act) which is or could be
         integrated with the sale of the Securities in a manner that would
         require the registration under the Act of the Securities or (ii)
         engaged in any form of general solicitation or general advertising (as
         those terms are used in Regulation D under the Act) in connection with
         the offering of the Securities or in any manner involving a public
         offering within the meaning of Section 4(2) of the Act.

                  (oo) When the Securities are delivered pursuant to this
         Agreement, none of the Securities will be of the same class (within the
         meaning of Rule 144A under the Act) as any other securities of the
         Issuer or any Guarantor that are listed on a national securities
         exchange registered under Section 6 of the Exchange Act or that are
         quoted in a United States automated inter-dealer quotation system.

                  (pp) Subsequent to the respective dates as of which
         information is given in the Final Memorandum and up to the Closing
         Date, except as set forth in the Final Memorandum, there has not been,
         individually or in the aggregate, any material adverse change, or any
         development which may reasonably be expected to involve a material
         adverse change, in the assets, properties, business, results of
         operations, condition (financial or otherwise), affairs or prospects of
         the Issuer and the Guarantors taken as a whole (including, without
         limitation, any material downward revision in the Issuer's estimated
         proved reserves) other than any such effect caused solely by decreases
         in crude oil, natural gas liquids and natural gas prices (any such
         event, a "Material Adverse Change").

                  (qq) Assuming that the representations and warranties of the
         Initial Purchaser contained in Section 8 are true and correct, it is
         not necessary in connection with the offer, sale and delivery of the
         Securities to the Initial Purchaser or the reoffer and resale by the
         Initial Purchaser in the manner contemplated by this Agreement to
         register the Securities under the Act or to qualify the Indenture in
         respect of the Notes under the TIA.

                  (rr) The form of the Security Documents, including the
         financing statements for the Mortgages (the "Financing Statements") and
         the form of acknowledgments thereto, comply with the laws of the
         jurisdiction where the property and interests covered by such documents
         are located, including all applicable recording, filing and
         registration laws and regulations, and are adequate and legally
         sufficient for the purposes intended to be accomplished thereby.

                  (ss) The descriptions of those portions of the Mortgaged
         Property (as defined in the Mortgages) or collateral which are
         described in the Mortgages are legally sufficient descriptions for the
         purpose of creating and maintaining the liens and security interests


                                       13
<PAGE>   14


         purported to be created by the Mortgages and for the purposes of all
         applicable recording, filing and registration laws in the jurisdiction
         where the property and interests covered by such documents are located.

                  (tt) Upon the recordings and filings as provided in the
         following paragraph, the Mortgages are effective to create in favor of
         the Trustee for the benefit of the Noteholders, as security for the
         payment of the Indebtedness (as defined in the Mortgages), a valid
         mortgage or deed of trust lien on all of the Issuer's and the
         Guarantors' right, title and interest in and to the portion of the
         Mortgaged Property constituting real property described in the
         Mortgages as being mortgaged thereby and a perfected security interest
         in all of the Issuer's and the Guarantors' right, title and interest in
         and to the portion of the Mortgaged Property constituting property,
         other than real property, in which a security interest can be created,
         and perfected by the filings contemplated by the following paragraph,
         under Article 9 of the Uniform Commercial Code as in effect in the
         States of Texas, Louisiana and California.

                  (uu) Fully executed counterparts of the Mortgages should be
         filed for record in each county or parish in the States of Texas,
         Louisiana and California where any portion of the Mortgaged Property is
         located (or, in the case of properties located on the Outer Continental
         Shelf, in the adjacent county or parish). Fully executed counterparts
         of the Financing Statements should be filed for record with the
         Secretary of State of the States of Texas and California and with the
         Parish Clerk of the Parish of East Baton Rouge, Louisiana. Other than
         the foregoing, no authorization, consent, approval, license or
         exemption of, or filing or registration with, any Governmental
         Authority of the States of Texas, Louisiana or California is necessary
         for either the due execution and delivery by the Issuer and the
         Guarantors of the Mortgages or the Financing Statements or with the
         holding and enforcement by the Trustee of the Mortgages secured
         thereby, except for such authorizations, consents, approvals, licenses
         or exemptions of, or filings or registrations with any Governmental
         Authority that are required to be obtained or maintained, as the case
         may be, by the Trustee in order for the Trustee to be or remain
         qualified to act in the capacity of trustee.

                  (vv) For so long as the Notes are outstanding and not matured,
         after the recordings and filings specified in the previous paragraph
         have occurred, no instruments need be recorded, registered or filed or
         re-recorded, re-registered or re-filed in any public office in the
         States of Texas, Louisiana or California in connection with the
         execution and delivery of the Mortgages or the Financing Statements in
         order to maintain the perfection and priority of the liens and security
         interests created thereby after the date of recordation, other than (i)
         that in the case of proceeds constituting a portion of the Mortgaged
         Property, continuation of perfection of the Trustee's security interest
         therein is limited to the extent set forth in the Uniform Commercial
         Code as in effect in the States of Texas, Louisiana and California,
         (ii) that in the case of property which becomes Mortgaged Property
         after the date hereof, 11 U.S.C. Section 552 limits the extent to which
         property acquired by a debtor after the commencement of a case under
         the United States Bankruptcy Code may be subject to a security interest
         arising from a security agreement entered into by the debtor before the
         commencement of such case, and (iii) continuation


                                       14
<PAGE>   15


         statements as required by the Uniform Commercial Code as in effect in
         the States of Texas, Louisiana and California.

                  (ww) No state or local recording tax, stamp tax or other
         similar fee, tax or governmental charge (other than statutory filing
         and recording fees to be paid upon the filing of the Mortgages or the
         Financing Statements) is required to be paid in connection with the
         filing and recording of the Mortgages or the Financing Statements.

                  (xx) The execution, delivery and performance of by the Issuer
         and each of the Guarantors of its obligations under the Mortgages will
         not result in a violation of any laws, rules and regulations of the
         States of Texas, Louisiana or California which are normally applicable
         to transactions of the type provided for in the Security Documents.

                  (yy) A state court of competent jurisdiction or a federal
         court sitting in the State of Texas, Louisiana or California of
         competent jurisdiction and applying conflicts of laws principles of
         such states, as applicable, if properly presented with a choice of law
         issue, should honor the choice of New York law to govern the Indenture
         and the other Security Documents that state such documents shall be
         governed by the laws of the State of New York, except to the extent the
         laws of other jurisdictions may be mandatorily applicable to certain
         matters under the Security Documents.

                  (zz) The representations and warranties of the Issuer and the
         Guarantors, as applicable, contained in Article IV of each of the
         Mortgages are true and correct and are hereby incorporated herein
         mutatis mutandis as representations and warranties of the Issuer and
         the Guarantors, respectively.

                  (aaa) The Company and the Subsidiary have negotiated
         definitive oil and gas production hedging agreements (the "Approved
         Hedging Agreements") with the Approved Hedge Counterparties (as defined
         in the Final Memorandum) party thereto as described under the heading
         "Description of Notes--Certain Covenants--Hedging Obligations" in the
         Final Memorandum.

         Any certificate signed by any officer of the Issuer or any Guarantor
and delivered to the Initial Purchaser or to counsel for the Initial Purchaser
shall be deemed a joint and several representation and warranty by the Issuer
and the Guarantors to the Initial Purchaser as to the matters covered thereby.

         3. Purchase, Sale and Delivery of the Securities. On the basis of the
representations, warranties, agreements and covenants herein contained and
subject to the terms and conditions set forth herein, the Issuer agrees to issue
and sell to the Initial Purchaser, and the Initial Purchaser agrees to purchase,
130,000 Units (and the related Guarantees) at a purchase price of $907.50 per
Unit, as described below. As additional consideration for services rendered by
the Initial Purchaser in connection with the transactions contemplated by this
Purchase Agreement, Tribo agrees to issue to the Initial Purchaser an aggregate
of 65,000 shares of Class B Common Stock. At the closing, (i) one or more
certificates representing the Units (comprised of a global Note and a global
certificate representing the Class A Common Stock) in definitive global form,
registered in the name of Cede & Co., as nominee of The Depository Trust Company
("DTC")


                                       15
<PAGE>   16


(the "Global Certificates"), (ii) one or more certificates representing the
Units (comprised of a certificated Note and a physical certificate representing
the Class A Common Stock) in certificated form and registered in the name of
such Persons as the Initial Purchaser shall designate prior to the Closing Date,
and (iii) a global certificate representing the Class B Common Stock, registered
in the name of Cede & Co., a nominee of DTC, shall be issued and delivered by
the Issuer and Tribo, as applicable, to the Initial Purchaser, against payment
by or on behalf of the Initial Purchaser of the purchase price therefore by wire
transfer (same-day funds) to such account or accounts as the Issuer and Tribo
shall specify prior to the Closing Date (or by such means as the parties hereto
shall agree prior to the Closing Date). Closing of the issuance, purchase, sale
and delivery of the Securities (the "Closing") shall take place at the offices
of Vinson & Elkins L.L.P., 2300 First City Tower, 1001 Fannin Street, Houston,
Texas 77002 at 8:00 a.m., central daylight time, on June 18, 2001, or such other
date, time or location as may be mutually acceptable, such time and date of
delivery against payment being referred to herein as the "Closing Date."

         4. Offering by the Initial Purchaser. The Initial Purchaser proposes to
make an offering of the Units at the price and upon the terms set forth in the
Final Memorandum, as soon as practicable after this Agreement is entered into
and as in the judgment of the Initial Purchaser is advisable.

         5. Covenants of the Issuer and the Guarantors. The Issuer and the
Guarantors, jointly and severally, covenant and agree with the Initial Purchaser
that:

                  (a) The Issuer and the Guarantors will not amend or supplement
         the Final Memorandum or any amendment or supplement thereto of which
         the Initial Purchaser shall not previously have been advised and
         furnished a copy for a reasonable period of time prior to the proposed
         amendment or supplement and as to which the Initial Purchaser shall not
         have given its consent, which consent shall not unreasonably be
         withheld. The Issuer and the Guarantors will promptly, upon the
         reasonable request of the Initial Purchaser or counsel for the Initial
         Purchaser, make any amendments or supplements to the Final Memorandum
         that may be necessary or advisable in connection with the resale of the
         Securities by the Initial Purchaser.

                  (b) The Issuer and the Guarantors will cooperate with the
         Initial Purchaser in arranging for the qualification of the Securities
         for offering and sale under the securities or "Blue Sky" laws of such
         jurisdictions as the Initial Purchaser may designate and will continue
         such qualifications in effect for as long as may be necessary to
         complete the resale of the Securities; provided, however, that in
         connection therewith, neither the Issuer nor the Guarantors shall be
         required to qualify as a foreign corporation or to execute a general
         consent to service of process in any jurisdiction or subject itself to
         taxation in excess of a nominal dollar amount in any such jurisdiction
         where it is not then so subject.

                  (c) If, at any time prior to the initial resale by the Initial
         Purchaser of the Units (and the related Guarantees) or the Exchange
         Notes, any event occurs or information becomes known as a result of
         which the Final Memorandum as then amended or supplemented would
         include any untrue statement of a material fact, or omit to state a


                                       16
<PAGE>   17


         material fact necessary to make the statements therein, in the light of
         the circumstances under which they were made, not misleading, or if for
         any other reason it is necessary at any time to amend or supplement the
         Final Memorandum to comply with applicable law, the Issuer will
         promptly notify the Initial Purchaser thereof and will prepare, at the
         expense of the Issuer, an amendment or supplement to the Final
         Memorandum that corrects such statement or omission or effects such
         compliance.

                  (d) The Issuer will, without charge, provide to the Initial
         Purchaser and to counsel for the Initial Purchaser as many copies of
         the Final Memorandum or any amendment or supplement thereto as the
         Initial Purchaser may reasonably request.

                  (e) The Issuer will apply the net proceeds from the sale of
         the Securities as set forth under "Use of Proceeds" in the Final
         Memorandum.

                  (f) For so long as any of the Securities (other than the
         Common Stock) remain outstanding, the Issuer and the Guarantors will
         furnish to the Initial Purchaser copies of all reports and other
         communications (financial or otherwise) furnished by the Issuer and the
         Guarantors to the Trustee or to the holders of the Securities and, as
         soon as available, copies of any reports or financial statements
         furnished to or filed by the Issuer or Tribo with the Commission or any
         national securities exchange on which any class of securities of the
         Issuer or Tribo may be listed.

                  (g) Prior to the Closing Date, Tribo will furnish to the
         Initial Purchaser, as soon as they have been prepared, if at all, a
         copy of any available unaudited consolidated interim financial
         statements of Tribo for any period subsequent to the period covered by
         the most recent financial statements of the Company appearing in the
         Final Memorandum.

                  (h) Neither the Issuer nor any of its Affiliates will sell,
         offer for sale or solicit offers to buy or otherwise negotiate in
         respect of any "security" (as defined in the Act) which could be
         integrated with the sale of the Securities in a manner which would
         require the registration under the Act of the Securities.

                  (i) The Issuer will not, and will not permit any of the
         Guarantors to, solicit any offer to buy or offer to sell the Securities
         by means of any form of general solicitation or general advertising (as
         those terms are used in Regulation D under the Act) or in any manner
         involving a public offering within the meaning of Section 4(2) of the
         Act.

                  (j) For so long as any of the Securities remain outstanding,
         the Company will make available at its expense, upon request, to any
         holder of such Securities and any prospective purchaser thereof, the
         information specified in Rule 144A(d)(4) under the Act, unless the
         Company is then subject to Section 13 or 15(d) of the Exchange Act.

                  (k) The Issuer will use its best efforts to (i) permit the
         Securities to be designated for trading in the Private Offerings,
         Resales and Trading through Automated Linkages market (the "PORTAL
         Market") of the NASD and (ii) permit the Securities to be eligible for
         clearance and settlement through DTC.


                                       17
<PAGE>   18


                  (l) The Issuer and each Guarantor will comply with their
         respective obligations under the Plan, the Confirmation Order and any
         Plan Documents (as defined in the Plan).

                  (m) Prior to the Closing Date, the Issuer and the Guarantors
         shall not modify or amend the Plan or the Confirmation Order without
         the written consent of the Initial Purchaser which consent shall not be
         unreasonably withheld.

                  (n) Concurrently with the Closing, the Company and the
         Subsidiary shall execute and deliver the Approved Hedging Agreements
         and shall execute one or more hedging transactions with the Approved
         Hedge Counterparties under the Approved Hedging Agreements.

                  (o) The Company will cure promptly any defects in the creation
         and issuance of the Securities and the execution and delivery of the
         Security Documents and any amendments thereto. At its expense, the
         Company will promptly execute and deliver to the Collateral Agent upon
         request all such other documents, agreements and instruments to comply
         with or accomplish the covenants and agreements of the Company in the
         Security Documents and any amendments thereto or to further evidence
         and more fully describe the collateral intended as security for the
         Notes, or to correct any omissions in the Security Documents and any
         amendments thereto, or to state more fully the security obligations set
         out herein or in any of the Security Documents or any amendments
         thereto, or to perfect, protect, preserve and maintain any liens
         created pursuant to any of the Security Documents or any amendments
         thereto and the first priority status of such liens (subject only to
         Permitted Liens (as defined in the Indenture)), or to make any
         recordings, to file any notices or obtain any consents, all as may be
         necessary or appropriate in connection therewith. The Company and the
         Guarantors will warrant and defend the first priority status of the
         liens created by the Security Documents and any amendments thereto,
         subject only to Permitted Liens.

                  (p) If delivery of the local counsel opinions required by
         Section 7(a)(ii) is waived by the Initial Purchaser on the Closing
         Date, then the Issuer shall deliver such local counsel opinions on or
         before the fifth business day following the Closing Date.

                  (q) To the extent waived by the Initial Purchaser on the
         Closing Date, the Issuer shall deliver the opinions of local counsel
         required by Section 7(a)(ii) of the Agreement on or before the fourth
         business day following the Closing Date.

                  (r) Each of the Company and the Guarantors shall use their
         best efforts to do and perform all things required or necessary to be
         done and performed under this Agreement by them prior to the Closing
         Date and to satisfy all conditions precedent to the delivery of the
         Securities.

         6. Fees and Expenses. The Issuer and the Guarantors agree, jointly and
severally, to pay all costs and expenses incident to the performance of their
respective obligations under this Agreement, whether or not the transactions
contemplated herein are consummated or this Agreement is terminated pursuant to
Section 11 hereof, including all costs and expenses incident


                                       18
<PAGE>   19


to (i) the printing, word processing or other production of documents with
respect to the transactions contemplated hereby, including any costs of printing
the Final Memorandum and any amendment or supplement thereto, and any "Blue Sky"
memoranda, (ii) all arrangements relating to the delivery to the Initial
Purchaser of copies of the foregoing documents, (iii) the fees and disbursements
of the counsel, the accountants and any other experts or advisors retained by
the Issuer, (iv) preparation (including printing), issuance and delivery to the
Initial Purchaser of the Securities, (v) the qualification of the Securities
under state securities and "Blue Sky" laws, including filing fees and reasonable
fees and disbursements of counsel for the Initial Purchaser relating thereto,
(vi) expenses in connection with any meetings with prospective investors in the
Securities, (vii) fees and expenses of the Trustee including reasonable fees and
expenses of its counsel, (viii) all expenses and listing fees incurred in
connection with the application for quotation of the Securities on the PORTAL
Market, (ix) any fees charged by investment rating agencies for the rating of
the Securities and (x) all reasonable fees, disbursements and out-of-pocket
expenses incurred by the Initial Purchaser in connection with the transactions
contemplated hereby (including fees and expenses of Vinson & Elkins L.L.P., as
counsel to the Initial Purchaser). If the sale of the Securities provided for
herein is not consummated because any condition to the obligations of the
Initial Purchaser set forth in Section 7 hereof is not satisfied, because this
Agreement is terminated or because of any failure, refusal or inability on the
part of the Issuer and the Guarantors to perform all obligations and satisfy all
conditions on their part to be performed or satisfied hereunder (other than
solely by reason of a default by the Initial Purchaser of its obligations
hereunder after all conditions hereunder have been satisfied in accordance
herewith), the Issuer and the Guarantors agree, jointly and severally, to
promptly reimburse the Initial Purchaser upon demand for all out-of-pocket
expenses that shall have been incurred by the Initial Purchaser in connection
with the proposed purchase and sale of the Securities. Additionally, the Issuer
and the Guarantors shall pay to the Initial Purchaser, on the Closing Date, a
financial advisory fee in the amount of $4,000,000 for financial advisory
services rendered by the Initial Purchaser to the Issuer and the Guarantors in
connection with the transactions contemplated by this Agreement.

         7. Conditions of the Initial Purchaser's Obligations. The obligation of
the Initial Purchaser to purchase and pay for the Securities shall, in its sole
discretion, be subject to the satisfaction or waiver of each of the following
conditions on or prior to the Closing Date:

                  (a) On the Closing Date, the Initial Purchaser shall have
         received the opinions, dated as of the Closing Date and addressed to
         the Initial Purchaser, of (i) Thompson & Knight LLP, counsel for the
         Issuer and the Guarantors, and (ii) local counsel for the Issuer and
         the Guarantors in the States of Louisiana and California, each in form
         and substance reasonably satisfactory to counsel for the Initial
         Purchaser, and each subject to customary assumptions and
         qualifications.

                  (b) On the Closing Date, the Initial Purchaser shall have
         received the opinion, in form and substance satisfactory to the Initial
         Purchaser, dated as of the Closing Date and addressed to the Initial
         Purchaser, of Vinson & Elkins L.L.P., counsel for the Initial
         Purchaser, with respect to certain legal matters relating to this
         Agreement and such other related matters as the Initial Purchaser may
         reasonably require.


                                       19
<PAGE>   20


                  (c) The Initial Purchaser shall have received from each of BDO
         Seidman, LLP and Hidalgo, Banfill, Zlotnik & Kermali, P.C. a comfort
         letter or letters dated the date hereof and dated as of the Closing
         Date, in form and substance satisfactory to the Initial Purchaser and
         its counsel.

                  (d) The representations and warranties of the Issuer and the
         Guarantors contained in this Agreement shall be true and correct in all
         material respects on and as of the date hereof and on and as of the
         Closing Date as if made on and as of the Closing Date (except for the
         representations and warranties that were true and correct as of a
         certain specified date, which shall continue to be true and correct as
         of such date); the statements of the Issuer's and the Guarantors'
         officers made pursuant to any certificate delivered in accordance with
         the provisions hereof shall be true and correct in all material
         respects on and as of the date made and on and as of the Closing Date;
         the Issuer and the Guarantors shall have performed all covenants and
         agreements and satisfied all conditions on their part to be performed
         or satisfied hereunder at or prior to the Closing Date; and, except as
         described in the Final Memorandum (exclusive of any amendment or
         supplement thereto after the date hereof), subsequent to the date of
         the most recent financial statements in such Final Memorandum, there
         shall have been no event or development, and no information shall have
         become known, that, individually or in the aggregate, has or would be
         reasonably likely to have a Material Adverse Effect.

                  (e) The sale of the Securities hereunder shall not be enjoined
         or stayed (temporarily or permanently) on the Closing Date.

                  (f) Subsequent to the date of the most recent financial
         statements in the Final Memorandum (exclusive of any amendment or
         supplement thereto after the date hereof), neither the Issuer nor any
         of the Guarantors shall have sustained any loss or interference with
         respect to its business or properties from fire, flood, hurricane,
         accident or other calamity, whether or not covered by insurance, or
         from any strike, labor dispute, slow down or work stoppage or from any
         legal or governmental proceeding, order or decree, which loss or
         interference, individually or in the aggregate, has or would be
         reasonably likely to have a Material Adverse Effect.

                  (g) The Initial Purchaser shall have received a certificate,
         dated the Closing Date, of the Company and each of the Guarantors,
         signed on behalf of the Company and each of the Guarantors by their
         respective Chairmen of the Board, Presidents or any Senior Vice
         Presidents and Chief Financial Officers, to the effect that:

                           (i) The representations and warranties of the Issuer
                  and the Guarantors, as applicable, contained in the Purchase
                  Agreement are true and correct on and as of the date hereof
                  and on and as of the Closing Date (except for the
                  representations and warranties that were true and correct as
                  of a certain specified date, which shall continue to be true
                  and correct as of such date), and the Issuer and the
                  Guarantors, as applicable, have performed all covenants and
                  agreements and satisfied all conditions on their part to be
                  performed or satisfied hereunder at or prior to the Closing
                  Date;


                                       20
<PAGE>   21


                           (ii) At the Closing Date, since the date hereof or
                  since the date of the most recent financial statements in the
                  Final Memorandum (exclusive of any amendment or supplement
                  thereto after the date hereof), no event or development has
                  occurred, and no information has become known to the Issuer or
                  the Guarantors, as applicable, that, individually or in the
                  aggregate, has or would be reasonably likely to have a
                  Material Adverse Effect (including, without limitation, any
                  material downward revision in the Issuer's or the Guarantors'
                  estimated proved reserves) other than any such effect caused
                  solely by decreases in the prices of crude oil, natural gas
                  liquids and natural gas; and

                           (iii) The sale of the Securities hereunder has not
                  been enjoined or stayed (temporarily or permanently).

                  (h) On the Closing Date, the Initial Purchaser shall have
         received each of the Notes Registration Rights Agreement and the Equity
         Registration Rights Agreement executed by the Issuer and each of the
         Guarantors.

                  (i) On or before the Closing Date, the Initial Purchaser and
         counsel for the Initial Purchaser shall have received from the Issuer
         and the Guarantors executed Security Documents.

                  (j) On or before the Closing Date, the Initial Purchaser shall
         have received from the Issuer and the Guarantors evidence of the
         unconditional release of the liens and security interests granted in
         favor of Credit Lyonnais on any property of Richard Bowman ("Bowman"),
         the Issuer and the Guarantors and the Issuer shall have, concurrently
         with the Closing, paid to Credit Lyonnais all amounts set forth in the
         Payoff Letter.

                  (k) On or before the Closing Date, the Initial Purchaser shall
         have received from the Issuer and the Guarantors evidence of the
         unconditional release of the liens and security interests granted on
         any property of Bowman, the Issuer and the Guarantors in favor of each
         of the creditors under Classes 2 and 3 of the Plan.

                  (l) On or before the Closing Date, the Initial Purchaser shall
         have received from the Issuer and the Guarantors evidence of the
         execution of the agreed order of dismissal with prejudice and mutual
         releases of the Lawsuits (as defined in the Confirmation Order) by the
         Lawsuit Parties (as defined in the Confirmation Order) as required by
         the Confirmation Order.

                  (m) Concurrently with the Closing, the Issuer shall have
         transferred to the Lien Agent an amount equal to the Initial Escrow
         Funding (as defined in the Plan).

                  (n) Concurrently with the Closing, the Issuer shall have
         transferred to the Disbursing Agent an amount equal to the Class 5
         Funding (as defined in the Plan).

                  (o) Concurrently with the Closing, the Issuer shall have
         certified to the Initial Purchaser that it has executed one or more
         hedging transactions with the Approved Hedge Counterparties under the
         Approved Hedging Agreements.


                                       21
<PAGE>   22


                  (p) On the Closing Date, the Initial Purchaser shall have
         received letters, dated as of the Closing Date and addressed to the
         Initial Purchaser, of Huddleston & Co., Inc. and DeGolyer and
         MacNaughton, independent petroleum engineers for the Company, in form
         and substance reasonably satisfactory to the Initial Purchaser.

                  (q) The Confirmation Order shall be a Final Order and
         consummation of the Plan shall not be enjoined or stayed (temporarily
         or permanently) on the Closing Date.

                  (r) On or before the Closing Date, the Initial Purchaser and
         counsel for the Initial Purchaser shall have received certified copies
         of the Plan, the Confirmation Order and the docket of the Bankruptcy
         Court after June 4, 2001 showing that the Confirmation Order is a Final
         Order.

                  (s) On or before the Closing Date, the Issuer shall have
         received executed withdrawal of claim forms from Bowman and Tribo
         whereby each of them withdrawal all of their respective claims filed in
         the Bankruptcy Case.

                  (t) On or before the Closing Date, the Issuer shall have (i)
         consummated the Receipt, Release and Settlement Agreement (as amended,
         the "MMS Settlement Agreement") between the Issuer and the United
         States of America, by and through the Department of the Interior,
         Minerals Management Service (the "MMS"), as approved by the Bankruptcy
         Court in the Confirmation Order, (ii) replaced Frontier (as defined in
         the MMS Settlement Agreement) with a surety approved by the United
         States Treasury, (iii) caused such replacement surety to issue new
         bonds as required by the terms of the MMS Settlement Agreement, (iv)
         entered into an indemnity agreement in favor of such replacement
         surety, (v) paid all amounts due and owing on the Closing Date under
         the MMS Settlement Agreement, and (vi) received executed withdrawal of
         claim forms from the MMS withdrawing all claims filed in the Bankruptcy
         Case.

                  (u) On or before the Closing Date, the Issuer shall have
         executed a disbursing services agreement with each of the Lien Agent
         and the Disbursing Agent.

                  (v) On or before the Closing Date, the Issuer shall have filed
         objections with the Bankruptcy Court to all Disputed Claims as required
         by the Plan.

                  (w) On or before the Closing Date, the Initial Purchaser and
         counsel for the Initial Purchaser shall have received such further
         documents, opinions, certificates, letters and schedules or instruments
         relating to the business, corporate, legal and financial affairs of the
         Issuer and the Guarantors as they shall have heretofore reasonably
         requested from the Issuer.

         All such documents, opinions, certificates, letters, schedules or
instruments delivered pursuant to this Agreement will comply with the provisions
hereof only if they are reasonably satisfactory in all material respects to the
Initial Purchaser and counsel for the Initial Purchaser. The Issuer shall
furnish or cause to be furnished to the Initial Purchaser such conformed copies
of such documents, opinions, certificates, letters, schedules and instruments in
such quantities as the Initial Purchaser shall reasonably request. If the
Initial Purchaser waives the satisfaction of any of the foregoing conditions on
or prior to the Closing Date, the Company shall use its best


                                       22
<PAGE>   23


efforts to cause such conditions to be satisfied within five business days
following the Closing Date.

         8. Offering of Units; Restrictions on Transfer. The Initial Purchaser
has advised the Issuer that it proposes to offer the Units (and the related
Guarantees) for sale upon the terms and conditions set forth in this Agreement
and in the Final Memorandum. The Initial Purchaser hereby represents and
warrants to, and agrees with, the Issuer and the Guarantors that the Initial
Purchaser (i) is purchasing the Units (and the related Guarantees) pursuant to a
private sale exempt from registration under the Act, (ii) has not solicited and
will not solicit offers for, or offer or sell, the Units (and the related
Guarantees) by means of any form of general solicitation or general advertising
or in any manner involving a public offering within the meaning of Section 4(2)
of the Act, and (iii) will solicit offers for the Units (and the related
Guarantees) only from, and will offer, sell or deliver the Units (and the
related Guarantees) as part of their initial offering only to, (A) persons whom
the Initial Purchaser reasonably believes to be qualified institutional buyers
as defined in Rule 144A promulgated under the Act ("QIBs"), or if any such
person is buying for one or more institutional accounts for which such person is
acting as fiduciary or agent, only when such person has represented to the
Initial Purchaser that each such account is a QIB, to whom notice has been given
that such sale or delivery is being made in reliance on Rule 144A, in each case,
in transactions under Rule 144A or (B) to a limited number of accredited
investors as defined in Rule 501(a)(1), (2), (3) or (7) promulgated under the
Act that make the representations to and agreements with the Company specified
in Annex A to the Final Memorandum in private sales exempt from registration
under the Act. The Initial Purchaser will deliver to each purchaser of the Units
(and the related Guarantees) in connection with its original distribution of the
Units (and the related Guarantees), a copy of the Final Memorandum, as amended
and supplemented at the date of such delivery.

         9. Indemnification and Contribution.

                  (a) The Issuer and the Guarantors agree, jointly and
severally, to indemnify and hold harmless the Initial Purchaser, its affiliates
and each person, if any, who controls the Initial Purchaser within the meaning
of Section 15 of the Act or Section 20 of the Exchange Act, against any losses,
claims, damages or liabilities to which the Initial Purchaser or such
controlling person may become subject under the Act, the Exchange Act or
otherwise, insofar as any such losses, claims, damages or liabilities (or
actions in respect thereof) arise out of or are based upon:

                           (i) any untrue statement or alleged untrue statement
                  of any material fact contained in the Final Memorandum or any
                  amendment or supplement thereto or any application or other
                  document, or any amendment or supplement thereto, executed by
                  the Issuer or based upon written information furnished by or
                  on behalf of the Issuer filed in any jurisdiction in order to
                  qualify the Securities under the securities or "Blue Sky" laws
                  thereof or filed with any securities association or securities
                  exchange (each an "Application"); or

                           (ii) the omission or alleged omission to state, in
                  the Final Memorandum or any amendment or supplement thereto or
                  any Application, a material fact required to be stated therein
                  or necessary to make the statements


                                       23
<PAGE>   24


                  therein, in the light of the circumstances under which they
                  were made, not misleading,

and will reimburse, as incurred, the Initial Purchaser, each such affiliate and
each such controlling person for any reasonable legal or other reasonable
expenses incurred by the Initial Purchaser, such affiliate or such controlling
person in connection with investigating, defending against or appearing as a
third-party witness in connection with any such loss, claim, damage, liability
or action; provided, however, that the Issuer and the Guarantors will not be
liable in any such case to the extent that any such loss, claim, damage, or
liability arises out of or is based upon any untrue statement or alleged untrue
statement or omission or alleged omission made in the Final Memorandum or any
amendment or supplement thereto or any Application in reliance upon and in
conformity with written information concerning the Initial Purchaser furnished
to the Issuer by the Initial Purchaser specifically for use therein. This
indemnity agreement will be in addition to any liability that the Issuer and the
Guarantors may otherwise have to the indemnified parties. The Issuer and the
Guarantors shall not be liable under this Section 9 for any settlement of any
claim or action effected without their prior written consent, which shall not be
unreasonably withheld.

                  The Initial Purchaser shall not, without the prior written
consent of the Issuer, effect any settlement or compromise of any pending or
threatened proceeding in respect of which the Issuer is or could have been a
party, or indemnity could have been sought hereunder by the Issuer, unless such
settlement (A) included an unconditional written release of the Issuer, in form
and substance reasonably satisfactory to the Issuer, from all liability on
claims that are the subject matter of such proceeding and (B) does not include
any statement as to an admission of fault, culpability or failure to act by or
on behalf of the Issuer.

                  (b) The Initial Purchaser agrees to indemnify and hold
harmless the Issuer and the Guarantors, their respective directors and their
respective officers and each person, if any, who controls the Issuer or the
Guarantors within the meaning of Section 15 of the Act or Section 20 of the
Exchange Act against any losses, claims, damages or liabilities to which the
Issuer or any of the Guarantors or any such director, officer or controlling
person may become subject under the Act, the Exchange Act or otherwise, insofar
as such losses, claims, damages or liabilities (or actions in respect thereof)
arise out of or are based upon (i) any untrue statement or alleged untrue
statement of any material fact contained in the Final Memorandum or any
amendment or supplement thereto or any Application, or (ii) the omission or the
alleged omission to state therein a material fact required to be stated in the
Final Memorandum or any amendment or supplement thereto or any Application, or
necessary to make the statements therein, in the light of the circumstances
under which they were made, not misleading, in each case to the extent, but only
to the extent, that such untrue statement or alleged untrue statement or
omission or alleged omission was made in reliance upon and in conformity with
written information concerning the Initial Purchaser, furnished to the Issuer by
the Initial Purchaser specifically for use therein; and subject to the
limitation set forth immediately preceding this clause, will reimburse, as
incurred, any reasonable legal or other expenses incurred by the Issuer or any
of the Guarantors or any such director, officer or controlling person in
connection with investigating or defending against or appearing as a third party
witness in connection with any such loss, claim, damage, liability or action in
respect thereof. This indemnity agreement will be in addition to any liability
that the Initial Purchaser may otherwise have to the indemnified


                                       24
<PAGE>   25


parties. The Initial Purchaser shall not be liable under this Section 9 for any
settlement of any claim or action effected without its consent, which shall not
be unreasonably withheld.

                  The Issuer shall not, without the prior written consent of the
Initial Purchaser, effect any settlement or compromise of any pending or
threatened proceeding in respect of which the Initial Purchaser is or could have
been a party, or indemnity could have been sought hereunder by the Initial
Purchaser, unless such settlement (A) includes an unconditional written release
of the Initial Purchaser, in form and substance reasonably satisfactory to the
Initial Purchaser, from all liability on claims that are the subject matter of
such proceeding and (B) does not include any statement as to an admission of
fault, culpability or failure to act by or on behalf of the Initial Purchaser.

                  (c) Promptly after receipt by an indemnified party under this
Section 9 of notice of the commencement of any action for which such indemnified
party is entitled to indemnification under this Section 9, such indemnified
party will, if a claim in respect thereof is to be made against the indemnifying
party under this Section 9, notify the indemnifying party of the commencement
thereof in writing; but the omission to so notify the indemnifying party (i)
will not relieve the indemnifying party from any liability under paragraph (a)
or (b) above unless and to the extent such failure results in the forfeiture by
the indemnifying party of substantial rights and defenses and (ii) will not, in
any event, relieve the indemnifying party from any obligations to any
indemnified party other than the indemnification obligation provided in
paragraphs (a) and (b) above. In case any such action is brought against any
indemnified party, and it notifies the indemnifying party of the commencement
thereof, the indemnifying party will be entitled to participate therein and, to
the extent that it may wish, jointly with any other indemnifying party similarly
notified, to assume the defense thereof, with counsel reasonably satisfactory to
such indemnified party; provided, however, that if (i) the use of counsel chosen
by the indemnifying party to represent the indemnified party would present such
counsel with a conflict of interest, (ii) the defendants in any such action
include both the indemnified party and the indemnifying party and the
indemnified party shall have been advised by counsel that there may be one or
more legal defenses available to it and/or other indemnified parties that are
different from or additional to those available to the indemnifying party, or
(iii) the indemnifying party shall not have employed counsel reasonably
satisfactory to the indemnified party to represent the indemnified party within
a reasonable time after receipt by the indemnifying party of notice of the
institution of such action, then, in each such case, the indemnifying party
shall not have the right to direct the defense of such action on behalf of such
indemnified party or parties and such indemnified party or parties shall have
the right to select separate counsel to defend such action on behalf of such
indemnified party or parties. After notice from the indemnifying party to such
indemnified party of its election so to assume the defense thereof and approval
by such indemnified party of counsel appointed to defend such action, the
indemnifying party will not be liable to such indemnified party under this
Section 9 for any legal or other expenses, other than reasonable costs of
investigation, subsequently incurred by such indemnified party in connection
with the defense thereof, unless (i) the indemnified party shall have employed
separate counsel in accordance with the proviso to the immediately preceding
sentence (it being understood, however, that in connection with such action the
indemnifying party shall not be liable for the expenses of more than one
separate counsel (in addition to local counsel) in any one action or separate
but substantially similar actions in the same jurisdiction arising out of the
same general allegations or circumstances, designated by the Initial Purchaser


                                       25
<PAGE>   26


in the case of paragraph (a) of this Section 9 or the Issuer in the case of
paragraph (b) of this Section 9, representing the indemnified parties under such
paragraph (a) or paragraph (b), as the case may be, who are parties to such
action or actions) or (ii) the indemnifying party has authorized in writing the
employment of counsel for the indemnified party at the expense of the
indemnifying party. After such notice from the indemnifying party to such
indemnified party, the indemnifying party will not be liable for the costs and
expenses of any settlement of such action effected by such indemnified party
without the prior written consent of the indemnifying party (which consent shall
not be unreasonably withheld), unless such indemnified party waived in writing
its rights under this Section 9, in which case the indemnified party may effect
such a settlement without such consent.

                  (d) In circumstances in which the indemnity agreement provided
for in the preceding paragraphs of this Section 9 is unavailable to, or
insufficient to hold harmless, an indemnified party in respect of any losses,
claims, damages or liabilities (or actions in respect thereof), each
indemnifying party, in order to provide for just and equitable contribution,
shall contribute to the amount paid or payable by such indemnified party as a
result of such losses, claims, damages or liabilities (or actions in respect
thereof) in such proportion as is appropriate to reflect (i) the relative
benefits received by the indemnifying party or parties on the one hand and the
indemnified party on the other from the offering of the Securities or (ii) if
the allocation provided by the foregoing clause (i) is not permitted by
applicable law, not only such relative benefits but also the relative fault of
the indemnifying party or parties on the one hand and the indemnified party on
the other in connection with the statements or omissions or alleged statements
or omissions that resulted in such losses, claims, damages or liabilities (or
actions in respect thereof). The relative benefits received by the Issuer on the
one hand and the Initial Purchaser on the other shall be deemed to be in the
same proportion as the total proceeds from the offering (before deducting
expenses) received by the Issuer bear to the total discounts and commissions
received by the Initial Purchaser. The relative fault of the parties shall be
determined by reference to, among other things, whether the untrue or alleged
untrue statement of a material fact or the omission or alleged omission to state
a material fact relates to information supplied by the Issuer on the one hand,
or the Initial Purchaser on the other, the parties' relative intent, knowledge,
access to information and opportunity to correct or prevent such statement or
omission or alleged statement or omission, and any other equitable
considerations appropriate in the circumstances. The Issuer and the Initial
Purchaser agree that it would not be equitable if the amount of such
contribution were determined by pro rata or per capita allocation or by any
other method of allocation that does not take into account the equitable
considerations referred to in the first sentence of this paragraph (d).
Notwithstanding any other provision of this paragraph (d), the Initial Purchaser
shall not be obligated to make contributions hereunder that in the aggregate
exceed the total discounts, commissions and other compensation received by the
Initial Purchaser under this Agreement, less the aggregate amount of any damages
that the Initial Purchaser has otherwise been required to pay by reason of the
untrue or alleged untrue statements or the omissions or alleged omissions to
state a material fact, and no person guilty of fraudulent misrepresentation
(within the meaning of Section 11(f) of the Act) shall be entitled to
contribution from any person who was not guilty of such fraudulent
misrepresentation. For purposes of this paragraph (d), each affiliate of the
Initial Purchaser, and each person, if any, who controls the Initial Purchaser
within the meaning of Section 15 of the Act or Section 20 of the Exchange Act,
shall have the same rights to contribution as the Initial Purchaser, and each
director of the Issuer, each officer of the Issuer and each person, if any, who


                                       26
<PAGE>   27


controls the Issuer within the meaning of Section 15 of the Act or Section 20 of
the Exchange Act, shall have the same rights to contribution as the Issuer.

         10. Survival Clause. The respective representations, warranties,
agreements, covenants, indemnities and other statements of the Issuer and the
Guarantors, their respective officers and the Initial Purchaser set forth in
this Agreement or made by or on behalf of them pursuant to this Agreement shall
remain in full force and effect, regardless of (i) any investigation made by or
on behalf of the Issuer and the Guarantors, any of their respective officers or
directors, the Initial Purchaser or any controlling person referred to in
Section 9 hereof and (ii) delivery of and payment for the Securities. The
respective agreements, covenants, indemnities and other statements set forth in
Sections 6, 9 and 15 hereof shall remain in full force and effect, regardless of
any termination or cancellation of this Agreement.

         11. Termination.

                  (a) This Agreement may be terminated in the sole discretion of
the Initial Purchaser by notice to the Issuer given prior to the Closing Date in
the event that the Issuer or any Guarantor shall have failed, refused or been
unable to perform all obligations and satisfy all conditions on its part to be
performed or satisfied hereunder at or prior thereto or, if at or prior to the
Closing Date:

                           (i) the Issuer or any of the Guarantors shall have
                  sustained any loss or interference with respect to its
                  businesses or properties from fire, flood, hurricane, accident
                  or other calamity, whether or not covered by insurance, or
                  from any strike, labor dispute, slow down or work stoppage or
                  any legal or governmental proceeding, which loss or
                  interference, in the sole judgment of the Initial Purchaser,
                  has had or has a Material Adverse Effect, or there shall have
                  been, in the sole judgment of the Initial Purchaser, any event
                  or development that, individually or in the aggregate, has or
                  could be reasonably likely to have a Material Adverse Effect
                  (including without limitation a change in control of any of
                  the Issuer or the Guarantors), except in each case as
                  described in the Final Memorandum (exclusive of any amendment
                  or supplement thereto);

                           (ii) trading in securities generally on the New York
                  Stock Exchange, American Stock Exchange or the NASDAQ National
                  Market shall have been suspended or minimum or maximum prices
                  shall have been established on any such exchange or market;

                           (iii) a banking moratorium shall have been declared
                  by New York or United States authorities;

                           (iv) there shall have been (A) an outbreak or
                  escalation of hostilities between the United States and any
                  foreign power, or (B) an outbreak or escalation of any other
                  insurrection or armed conflict involving the United States or
                  any other national or international calamity or emergency, or
                  (C) any material change in the financial markets of the United
                  States which, in the case of (A), (B) or (C) above and in the
                  sole judgment of the Initial Purchaser, makes it impracticable
                  or


                                       27
<PAGE>   28


                  inadvisable to proceed with the offering or the delivery of
                  the Securities as contemplated by the Final Memorandum;

                           (v) the Notes fail to receive a rating or, if the
                  Notes have received such rating, are thereafter downgraded
                  such that the Notes are rated below "B-3" by Moody's Investors
                  Service, Inc. or "B-" by Standard & Poor's Ratings Services;

                           (vi) an order is entered in the Bankruptcy Case
                  converting the Bankruptcy Case to a case under Chapter 7 of
                  the United States Bankruptcy Code, appointing a trustee or
                  examiner in the Bankruptcy Case pursuant to 11 U.S.C. Section
                  1104, dismissing the Bankruptcy Case or granting relief from
                  the automatic stay of Section 362 to allow any person or
                  entity to enforce any lien or security interest in any portion
                  of the Issuer's assets or properties; or

                           (vii) the Confirmation Order shall have been revoked
                  or vacated.

                  (b) Termination of this Agreement pursuant to this Section 11
shall be without liability of any party to any other party except as provided in
Section 10 hereof.

         12. Information Supplied by the Initial Purchaser. The statements set
forth in the last paragraph on the front cover page, the paragraph regarding
stabilization on page i, the first and third sentences of the third paragraph,
the fourth and sixth paragraphs, the fifth and sixth sentences of the seventh
paragraph and the eighth paragraph under the heading "Plan of Distribution" in
the Final Memorandum (to the extent such statements relate to the Initial
Purchaser) constitute the only information furnished by the Initial Purchaser to
the Issuer for the purposes of Sections 2(a) and 9 hereof and the Initial
Purchaser confirms that such statements are correct as of the date hereof and as
of the Closing Date.

         13. Notices. All communications hereunder shall be in writing and, if
sent to the Initial Purchaser, shall be mailed or delivered to Jefferies &
Company, Inc., 909 Fannin, Suite 3100, Houston, Texas 77010, Attention: Todd A.
Dittmann, with a copy to Vinson & Elkins L.L.P., 1001 Fannin, Suite 2300,
Houston, Texas 77002-6760, Attention: T. Mark Kelly; if sent to the Issuer or
the Guarantors, if any, shall be mailed or delivered to the Issuer at 530 Lovett
Boulevard, Houston, Texas 77006-4021, Attention: R. Kelly Plato, with a copy to
Thompson & Knight, LLP, 1200 Smith Street, Suite 1600, Houston, Texas 77002,
Attention: Barry Davis.

         All such notices and communications shall be deemed to have been duly
given: when delivered by hand, if personally delivered; five business days after
being deposited in the mail, postage prepaid, if mailed; and one business day
after being timely delivered to a next-day air courier.

         14. Successors. This Agreement shall inure to the benefit of and be
binding upon the Initial Purchaser, the Issuer and the Guarantors and their
respective successors and legal representatives, and nothing expressed or
mentioned in this Agreement is intended or shall be construed to give any other
person any legal or equitable right, remedy or claim under or in respect of this
Agreement, or any provisions herein contained; this Agreement and all conditions
and provisions hereof being intended to be and being for the sole and exclusive
benefit of such persons and for the benefit of no other person except that (i)
the indemnities of the Issuer and the


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<PAGE>   29


Guarantors contained in Section 9 of this Agreement shall also be for the
benefit of any person or persons who control the Initial Purchaser within the
meaning of Section 15 of the Act or Section 20 of the Exchange Act and (ii) the
indemnities of the Initial Purchaser contained in Section 9 of this Agreement
shall also be for the benefit of the directors of the Issuer and the Guarantors,
if any, their respective officers and any person or persons who control the
Issuer within the meaning of Section 15 of the Act or Section 20 of the Exchange
Act. No purchaser of Securities from the Initial Purchaser will be deemed a
successor because of such purchase.

         15. APPLICABLE LAW. THE VALIDITY AND INTERPRETATION OF THIS AGREEMENT,
AND THE TERMS AND CONDITIONS SET FORTH HEREIN SHALL BE GOVERNED BY AND CONSTRUED
IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK APPLICABLE TO CONTRACTS
MADE AND TO BE PERFORMED WHOLLY THEREIN, WITHOUT GIVING EFFECT TO ANY PROVISIONS
THEREOF RELATING TO CONFLICTS OF LAW.

         16. Counterparts. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.


                                       29
<PAGE>   30


         If the foregoing correctly sets forth our understanding, please
indicate your acceptance thereof in the space provided below for that purpose,
whereupon this letter, which has been executed on June 13, 2001, shall
constitute a binding agreement between the Issuer, the Guarantors and the
Initial Purchaser.

                                             Very truly yours,

                                             TRI-UNION DEVELOPMENT CORPORATION


                                             ---------------------------------
                                             Richard Bowman, President


                                             TRI-UNION OPERATING COMPANY


                                             ---------------------------------
                                             Richard Bowman, President


                                             TRIBO PETROLEUM CORPORATION


                                             ---------------------------------
                                             Richard Bowman, President


The foregoing Agreement is hereby
confirmed and accepted on June 13, 2001.

JEFFERIES & COMPANY INC.


By:
   -------------------------------------
Name:
Title:


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