<PAGE>

                                                                    EXHIBIT 10.1

                              FIRST AMENDMENT TO

                   NATURAL GAS PREPAID FORWARD SALE CONTRACT

     This FIRST AMENDMENT TO NATURAL GAS PREPAID FORWARD SALE CONTRACT (this
"Amendment") is entered into as of May 16, 2000, by and between EEX E&P Company,
L.P., a Delaware limited partnership, formerly known as Tesoro E&P Company,
L.P., having its principal place of business in Houston, Texas (hereinafter
referred to as the "Seller"), and Bob West Treasure L.L.C., a Delaware limited
liability company and having its principal place of business in Houston, Texas
(hereinafter referred to as the "Purchaser").

     WHEREAS, Purchaser and Seller have entered into that certain Natural Gas
Prepaid Forward Sale Contract dated December 17, 1999 (said Natural Gas Prepaid
Forward Sale Contract, as it may be amended, amended and restated or otherwise
modified from time to time, the "Gas Sale Contract") under the terms of which
Purchaser agreed to purchase certain quantities of Natural Gas on the terms and
conditions set forth therein; and

     WHEREAS, Purchaser and Seller have agreed to amend the Gas Sale Contract
pursuant to the terms contained in this Amendment;

     NOW THEREFORE, in consideration of the respective covenants and agreements
of the parties hereinafter set forth and for good and valuable consideration
(the receipt and sufficiency of which are hereby acknowledged by each of the
parties), the parties hereby agree as follows:

        1. DEFINITIONS (a) For purposes of this Agreement, all capitalized terms
not otherwise defined herein shall have the meanings as defined in the Gas Sale
Contract as amended by this Amendment:

          (b) The definition of "Mortgage" is hereby restated in its entirety to
read as follows:

               "Mortgage" shall mean (a) that certain Mortgage, Deed of Trust,
          Assignment of Production, Security Agreement and Financing Statement,
          dated the date of this Agreement executed and delivery by Seller, as
          mortgagor, for the benefit of Purchaser, as mortgagee covering all of
          Seller's interest in certain Designated Properties located in the
          State of Texas, together with all related accounts, equipment, oil and
          gas inventory, fixtures, contract rights, general intangibles and all
          proceeds of any of the foregoing, as amended and supplemented by that
          certain Amendment and Supplement to Mortgage, Deed of Trust,
          Assignment of Production, Security Agreement and Financing Statement
          dated May 16, 2000 between Seller and Purchaser and as such may be
          further modified, amended, amended and restated or otherwise
          supplemented from time to time, and (b) that certain Act of Mortgage,
          Assignment of Production, Security Agreement and Financing Statement,
          dated the date of this Agreement executed and delivery by Seller, as
          mortgagor, for the benefit of Purchaser, as mortgagee covering all of
          Seller's interest in certain
<PAGE>

          Designated Properties located in or offshore the State of Louisiana,
          together with all related accounts, equipment, oil and gas inventory,
          fixtures, contract rights, general intangibles and all proceeds of any
          of the foregoing, as amended by that certain Amendment to Act of
          Mortgage, Assignment of Production, Security Agreement and Financing
          Statement dated May 16, 2000 between Seller and Purchaser and as such
          may be further modified, amended, amended and restated or otherwise
          supplemented from time to time; and (c) that certain Mortgage, Deed of
          Trust, Assignment of Production, Security Agreement and Fixture
          Filing, dated May 16, 2000, executed and delivery by Seller, as
          mortgagor, for the benefit of Purchaser, as mortgagee, covering all of
          Seller's interest in certain Designated Properties located in the
          State of Texas, together with all related accounts, equipment, oil and
          gas inventory, fixtures, contract rights, general intangibles and all
          proceeds of any of the foregoing, as such may be modified, amended,
          amended and restated or otherwise supplemented from time to time.

        2. AMENDMENT TO SECTION 5.02 Section 5.02(d) of the Gas Sale Contract is
hereby restated in its entirety to read as follows:

               "(d)  DEBT.  Seller will not (i) incur any debt for borrowed
          money (whether by loan or the issuance and sale of debt securities),
          (ii) enter into any deferred sale agreement or capital lease, (iii)
          enter into any other obligation, contingent or otherwise, guaranteeing
          or having the economic effect of guaranteeing any debt or other
          obligations of any other Person in any manner, whether direct or
          indirect or (iv) incur any other obligation or liability in respect of
          any hedging agreement or any swap agreement, other than:  (A) any swap
          agreement entered into with ENA and (B) any swap agreement with any
          third party which, together with all other swap agreements (including
          those with ENA) covers eighty percent (80%) or less of the total
          production of oil and gas from all properties owned by Seller;
          provided that Seller may incur debt for borrowed money which is
          subordinated on terms generally comparable to those contained in that
          certain Subordinated Note dated December 17, 1999 executed by EEX
          Reserves Funding in the face amount  of $176,277,533 with a discounted
          principal amount of $100,000,000, which terms, among other items, (A)
          will not require or permit any principal payment or any cash interest
          payment thereon of any kind, but (B) which may require or permit
          payment of interest in kind and (C) may provide for conversion of such
          debt to equity in EEX Reserves Funding, after all of Seller's
          obligations under this Agreement and the Definitive Agreements have
          been satisfied in full."

        4. SCHEDULES. Any reference in the Gas Sale Agreement to Schedule
4.01(n), Schedule 4.01(o)(i), Schedule 4.01(p) or Schedule 4.01(q) shall be a
reference to Schedule 4.01(n), Schedule 4.01(o)(i), Schedule 4.01(p) or Schedule
4.01(q), respectively, attached to this Amendment.
<PAGE>

        5. RATIFICATION. Each of the Purchaser and the Seller hereby ratifies
all of its obligations under the Gas Sale Contract and agrees and acknowledges
that the Gas Sale Contract shall continue in full force and effect as amended
and modified by this Amendment. EEX Corporation, a Texas corporation ("EEX"),
joins in this Amendment for the purposes of acknowledging the amendment of the
Gas Sales Contract and ratifying its obligations under that certain EEX
Corporation Undertaking dated December 17, 1999, executed by EEX in favor of
Purchaser and for no other purpose.

        6. REPRESENTATIONS AND WARRANTIES. Each of the Purchaser and the Seller
hereby represents and warrants, respectively, that (a) this Amendment has been
duly executed and delivered on behalf of such Person, (b) this Amendment
constitutes a valid and legally binding agreement enforceable against such
Person in accordance with its terms, (c) the representations and warranties
contained in the Gas Sale Agreement are true and correct on and as of the date
hereof in all material respects as though made as of the date hereof, (d) no
Default or Event of Default exists under the Gas Sale Agreement or under any of
Loan Document and (e) the execution, delivery and performance of this Amendment
has been duly authorized by such Person. EEX hereby represents and warrants that
(a) the obligation of EEX under this Amendment has been duly executed and
delivered on behalf of such Person, (b) this Amendment constitutes a valid and
legally binding agreement enforceable against such Person in accordance with its
terms and (c) the execution and delivery of this Amendment has been duly
authorized by such Person.

        7. CONDITIONS TO EFFECTIVENESS. This Amendment shall be effective upon
the execution and delivery hereof by each of the Purchaser and the Seller.

        8. COUNTERPARTS. This Amendment may be signed in any number of
counterparts, which may be delivered in original or facsimile form each of which
shall be construed as an original, but all of which together shall constitute
one and the same instrument.

        9. GOVERNING LAW.  This Agreement shall be governed by and construed in
accordance with the laws of the State of Texas, without giving effect to
principles of conflicts of laws that would result in the application of the laws
of another jurisdiction.

        10. ENTIRE AGREEMENT. This Amendment, the Gas Sale Agreement and thE
Definitive Agreements constitute the entire agreement between the parties hereto
with respect to the subject hereof and supersede any prior agreement,
undertaking, declarations, commitments or representations, written or oral, in
respect thereof.

                    [Remainder of Page Intentionally Blank]
<PAGE>

        IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their respective officers thereunto duly authorized as of the date
first above written.


                                 SELLER
                                 ------

                                 EEX E&P COMPANY, L.P. (formerly known as Tesoro
                                 E&P Company, L.P.)

                                 By:  EEX Exploration & Production Company, LLC
                                      (formerly known as Tesoro Exploration &
                                      Production Company, LLC), its General
                                      Partner



                                  By:    /s/ J. T. Leary
                                      ----------------------------------
                                      J. T. Leary
                                      Vice President

          The undersigned is a party to this Amendment to acknowledge the
representations and ratification made by EEX in Paragraphs 5 and 6 above.

                                EEX CORPORATION


                                By:    /s/ J. T. Leary
                                    -------------------------------
                                    J. T. Leary
                                    Vice President, Finance and Treasurer
<PAGE>

                                PURCHASER
                                ---------

                                BOB WEST TREASURE L.L.C.

                                By:  Enron North America Corp.,
                                     its managing member


                                     By:    /s/ James R. McBride
                                         ----------------------------
                                         James R. McBride
                                         Vice President