<PAGE>
 
                                                                   Exhibit 10.22

                                 CONFIRMATION

                                COMMODITY SWAP
                                 CASH SETTLED

DATE:  SEPTEMBER 1, 1996

TO:     CHEVRON U.S.A. INC. ("CHEVRON")

ATTN:   MIDSTREAM BUSINESS UNIT ALLIANCE MANAGER (CPDN)

FROM:   NATURAL GAS CLEARINGHOUSE ("NGC")

The purpose of this document is to confirm the terms and conditions of the
Transaction entered into by NGC and Chevron on the trade date specified below.
This document constitutes a "Confirmation" as defined in the Master Agreement
specified below. This Confirmation supplements, forms a part of and is subject
to the Master Agreement dated as of February 1, 1993 executed by NGC and
Chevron. The terms and conditions of the Master Agreement govern this
Confirmation except as specifically provided below.

The terms and conditions of the Transaction relating to this Confirmation are as
follows:
 
COMMODITY:                      NATURAL GAS 

NOTIONAL QUANTITY PER           EXCEPT AS PROVIDED IN PARAGRAPH 4.
CALCULATION PERIOD:             OF "OTHER CONDITIONS" BELOW, THE MONTHLY
                                QUANTITY OF NATURAL GAS DELIVERED BY CHEVRON TO
                                LONE STAR GAS COMPANY ("LONE STAR") FOR
                                CHEVRON'S ACCOUNT PURSUANT TO THAT CERTAIN GAS
                                PURCHASE AGREEMENT DATED JULY 27 1955, AS
                                AMENDED, BETWEEN CHEVRON'S PREDECESSOR, STANDARD
                                OIL COMPANY OF TEXAS, AS SELLER, AND LONE STAR,
                                AS BUYER (THE "LONE STAR CONTRACT"), LESS THIRTY
                                SIX PERCENT (36%) OF THE MONTHLY QUANTITY OF
                                NATURAL GAS PRODUCED FROM AND ATTRIBUTABLE TO
                                CHEVRON'S OWNERSHIP INTEREST IN WELLS LOCATED ON
                                THE ACREAGE DEDICATED TO THE LONE STAR CONTRACT
                                ("CHEVRON'S OWN PRODUCTION") AND DELIVERED BY
                                CHEVRON TO LONE STAR PURSUANT TO THE LONE STAR
                                CONTRACT. THE NOTIONAL QUANTITY SHALL INCLUDE
                                SIXTY FOUR PERCENT (64%) OF THE NATURAL GAS
                                DELIVERED BY CHEVRON

                                       1
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                                PURSUANT TO THE LONE STAR CONTRACT FROM
                                CHEVRON'S OWN PRODUCTION AND ONE HUNDRED PERCENT
                                (100%) OF TH NATURAL GAS PURCHASED BY CHEVRON
                                FROM THIRD PARTIES ("THIRD PARTY PRODUCTION")
                                AND DELIVERED TO LONE STAR PURSUANT TO THE LONE
                                STAR CONTRACT, BUT SHALL NOT INCLUDE ANY
                                QUANTITIES OF NATURAL GAS DELIVERED T LONE STAR
                                UNDER THE LONE STAR CONTRACT FOR WHICH CHEVRON
                                DOES NOT RECEIVE PAYMENT, INCLUDING, BUT NOT
                                LIMITED TO, QUANTITIES DELIVERED UNDER THE LONE
                                STAR CONTRACT BY PARTIES WHICH PRIOR TO MAY 17,
                                1996, ACQUIRED FROM CHEVRON PROPERTIES OR
                                INTERESTS IN PROPERTIES SUBJECT TO THE LONE STAR
                                CONTRACT.

TRADE DATE:                     SEPTEMBER 1, 1996
 
EFFECTIVE DATE:                 SEPTEMBER 1, 1996
 
TERMINATION DATE:               FIRST DAY OF THE MONTH FOLLOWING TERMINATION OF
                                LONE STAR CONTRACT
 
CALCULATION PERIOD(S):          EACH CALENDAR MONTH DURING THE TERM OF THE LONE
                                STAR CONTRACT
 
PAYMENT DATE:                   ON OR BEFORE THE LAST DAY OF THE MONTH 
                                FOLLOWING PHYSICAL DELIVERY OF NATURAL GAS UNDER
                                THE LONE STAR CONTRACT

FIXED AMOUNT DETAILS:

     FIXED PRICE PAYER:         CHEVRON

     FIXED AMOUNT:              THE PRICE PAID BY LONE STAR TO CHEVRON DURING
                                THE CALCULATION PERIOD FOR NATURAL GAS DELIVERED
                                PURSUANT TO THE LONE STAR CONTRACT. A COPY OF
                                THE PRICING PROVISION OF THE LONE STAR CONTRACT
                                IS ATTACHED HERETO AS EXHIBIT "A".

FLOATING AMOUNT DETAILS:

     FLOATING PRICE PAYER:      NGC

     FLOATING AMOUNT:           THE INDEX PRICE REPORTED IN THE FIRST ISSUE OF
                                INSIDE F.E.R.C.'S GAS MARKET REPORT PUBLISHED
                                DURING THE CALCULATION PERIOD IN THE TABLE
                                TITLED "DELIVERED SPOT-GAS PRICES" UNDER THE
                                HEADING "HOUSTON SHIP CHANNEL/BEAUMONT, TEXAS -
                                INDEX (LARGE PACKAGES ONLY) MINUS $0.15 PER
                                MMBTU.

                                       2
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OTHER CONDITIONS:               1. IF DURING ANY CALCULATION PERIOD CHEVRON
                                DELIVERS NATURAL GAS TO LONE STAR PURSUANT TO
                                THE LONE STAR CONTRACT, BUT LONE STAR FAILS TO
                                PAY CHEVRON FOR ALL OF SUCH NATURAL GAS, THE
                                NOTIONAL QUANTITY APPLICABLE TO THAT CALCULATION
                                PERIOD SHALL BE REDUCED BY A QUANTITY EQUAL TO
                                THE QUANTITY DELIVERED BY CHEVRON TO LONE STAR
                                BUT NOT PAID FOR BY LONE STAR. IF LONE STAR
                                SUBSEQUENTLY PAYS FOR SUCH NATURAL GAS, THE
                                NOTIONAL QUANTITY APPLICABLE TO THE CALCULATION
                                PERIOD DURING WHICH THE NATURAL GAS WAS
                                DELIVERED BY CHEVRON TO LONE STAR SHALL BE
                                RETROACTIVELY INCREASED TO REFLECT THE
                                QUANTITIES PAID FOR, AND APPROPRIATE ADJUSTMENTS
                                IN PAYMENTS DUE UNDER THIS TRANSACTION SHALL BE
                                MADE WITHIN TEN DAYS. CHEVRON AGREES TO
                                DILIGENTLY PURSUE PAYMENT IN SUCH INSTANCES.

                                2. IF DURING ANY CALCULATION PERIOD CHEVRON
                                DELIVERS NATURAL GAS TO LONE STAR PURSUANT TO
                                THE LONE STAR CONTRACT AND LONE STAR PAYS
                                CHEVRON FOR SUCH NATURAL GAS AT A PRICE LOWER
                                THAN THAT PROVIDED FOR IN THE LONE STAR
                                CONTRACT, THE FIXED AMOUNT APPLICABLE TO THAT
                                CALCULATION PERIOD SHALL BE THE AMOUNT ACTUALLY
                                PAID BY LONE STAR. IF LONE STAR SUBSEQUENTLY
                                PAYS THE ADDITIONAL AMOUNT DUE FOR SUCH NATURAL
                                GAS, THE FIXED AMOUNT APPLICABLE TO THE
                                CALCULATION PERIOD DURING WHICH THE NATURAL GAS
                                WAS DELIVERED BY CHEVRON TO LONE STAR SHALL BE
                                RETROACTIVELY INCREASED TO REFLECT THE FULL
                                PRICE PAID BY LONE STAR, AND APPROPRIATE
                                ADJUSTMENTS IN PAYMENTS UNDER THIS TRANSACTION
                                SHALL BE MADE WITHIN TEN DAYS. CHEVRON AGREES TO
                                DILIGENTLY PURSUE FULL PAYMENT FROM LONE STAR IN
                                SUCH INSTANCES.

                                3. CHEVRON AGREES THAT IT WILL NOT, WITHOUT
                                NGC'S PRIOR WRITTEN CONSENT, AMEND OR MODIFY THE
                                LONE STAR CONTRACT AFTER MAY 17, 1996, IN ANY
                                MANNER WHICH WOULD AFFECT THE AMOUNTS PAYABLE BY
                                EITHER CHEVRON OR NGC UNDER THIS TRANSACTION. IN
                                ADDITION, CHEVRON AGREES THAT IT WILL NOT, AFTER
                                MAY 17, 1996, SELL, FARMOUT, OR OTHERWISE
                                DISPOSE OF ANY PROPERTY OR INTEREST IN PROPERTY
                                SUBJECT TO THE LONE STAR CONTRACT WITHOUT
                                RESERVING AND EXERCISING A CALL ON NATURAL GAS
                                PRODUCTION WHICH WILL ALLOW CHEVRON TO CONTINUE
                                TO SELL NATURAL GAS FROM SUCH PROPERTY OR
                                INTEREST TO LONE STAR UNDER THE LONE STAR
                                CONTRACT. NOTHING HEREIN SHALL PREVENT CHEVRON,
                                ACTING AS A PRUDENT OPERATOR, FROM RELEASING,
                                CEASING TO OPERATE, OR ABANDONING ANY LEASE OR
                                PROPERTY SUBJECT TO THE LONE STAR CONTRACT IF,
                                IN CHEVRON'S SOLE DISCRETION, CONTINUING TO
                                OPERATE SUCH LEASE OR PROPERTY WOULD BE
                                UNECONOMICAL FOR CHEVRON.

                                       3
<PAGE>
 
                                4. IN THE EVENT WARREN PETROLEUM COMPANY,
                                LIMITED PARTNERSHIP ("WARREN") SELLS THE SHERMAN
                                PLANT AND EXERCISES ITS OPTION UNDER THAT
                                CERTAIN GAS PROCESSING AGREEMENT DATED AS OF
                                SEPTEMBER 1, 1996, BETWEEN CHEVRON AND WARREN,
                                TO REDUCE THE PROCESSING FEE AS PROVIDED IN
                                SECTION 2.3 OF THAT AGREEMENT, THE NOTIONAL
                                QUANTITY PER CALCULATION PERIOD UNDER THIS
                                CONFIRMATION, AND THE TRANSACTION FORMING THE
                                BASIS OF THIS CONFIRMATION, SHALL AUTOMATICALLY
                                CHANGE TO ONE HUNDRED PERCENT (100%) OF
                                CHEVRON'S OWN PRODUCTION AND ONE HUNDRED PERCENT
                                (100%) OF THIRD PARTY PRODUCTION DELIVERED BY
                                CHEVRON TO LONE STAR FOR CHEVRON'S ACCOUNT EACH
                                MONTH PURSUANT TO THE LONE STAR CONTRACT, LESS
                                ANY QUANTITIES OF NATURAL GAS DELIVERED TO LONE
                                STAR UNDER THE LONE STAR CONTRACT FOR WHICH
                                CHEVRON DOES NOT RECEIVE PAYMENT, INCLUDING, BUT
                                NOT LIMITED TO, QUANTITIES DELIVERED UNDER THE
                                LONE STAR CONTRACT BY PARTIES WHICH, PRIOR TO
                                MAY 17, 1996, ACQUIRED FROM CHEVRON PROPERTIES
                                OR INTERESTS IN PROPERTIES SUBJECT TO THE LONE
                                STAR CONTRACT.


          If this Confirmation correctly sets forth the terms of the Transaction
specified above, please so indicate by signing below and sending this
Confirmation (or a copy) to us.

          If this Confirmation contains any error, please notify NGC
immediately. Failure to Notify NGC of an error in this Confirmation or failure
to accept this Confirmation as provided in Master Agreement-Schedule Part 4(e)
after receipt by Chevron shall result in this Confirmation being deemed binding
as sent as set forth in the Master Agreement.

                                                Sincerely,

                                                Natural Gas Clearinghouse

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

AGREED TO AND ACCEPTED

----------------------------
By:  Chevron U.S.A. Inc.
Name:
Title:
Date:

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