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                                                                   EXHIBIT 10.54


                           GAS AND NATURAL GAS LIQUIDS
                               PURCHASE AGREEMENT


                              DATED MARCH 14, 2000


                                     BETWEEN



                        SOUTHERN PRODUCER SERVICES, L.P.,
                                   AS "BUYER"

                                       AND

                           TRANSTEXAS GAS CORPORATION,
                                   AS "SELLER"


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                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                                               PAGE
                                                                                                               ----
<S>                 <C>                                                                                        <C>
ARTICLE I.          DEDICATION AND QUANTITY.......................................................................2

ARTICLE II.         PRICE OF GAS AND NATURAL GAS LIQUIDS..........................................................4

ARTICLE III.        SELLER'S POINT(S) OF DELIVERY.................................................................5

ARTICLE IV.         TERM..........................................................................................5

ARTICLE V.          NOTICES.......................................................................................5

ARTICLE VI.         GENERAL.......................................................................................6

EXHIBIT "A".....................................................................................................A-1
         Section I.        Definitions..........................................................................A-1
         Section II.       Transportation, Processing and Dehydration/Treating..................................A-9
         Section III.      Measuring Equipment and Testing......................................................A-9
         Section IV.       Measurement Specifications..........................................................A-11
         Section V.        Quality.............................................................................A-11
         Section VI.       Delivery Pressure...................................................................A-11
         Section VII.      Taxes...............................................................................A-12
         Section VIII.     Billings and Payments...............................................................A-12
         Section IX.       Title, Possession and Responsibility................................................A-13
         Section X.        Warranty of Title...................................................................A-14
         Section XI.       Force Majeure.......................................................................A-14
         Section XII.      Remedy for Breach...................................................................A-16
         Section XIII.     Assignment..........................................................................A-17
         Section XIV.      Laws and Regulations................................................................A-17
         Section XV.       [Reserved]..........................................................................A-18
         Section XVI.      Miscellaneous.......................................................................A-18

EXHIBIT "B"

EXHIBIT "C"
</TABLE>


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                 GAS AND NATURAL GAS LIQUIDS PURCHASE AGREEMENT

         THIS GAS AND NATURAL GAS LIQUIDS PURCHASE AGREEMENT (herein called this
"Agreement") is made and entered into as of the 14th Day of March, 2000, by and
between SOUTHERN PRODUCER SERVICES, L.P., a Delaware limited partnership (herein
called the "Buyer") and TRANSTEXAS GAS CORPORATION, a Delaware corporation
herein called the "Seller"). Buyer and Seller are sometimes referred to
singularly as "Party" and collectively as "Parties". Certain capitalized terms
used herein are defined as set forth in Exhibit A hereto or as otherwise
indicated.

                                   WITNESSETH:

         WHEREAS, Seller has heretofore filed for protection under Chapter 11 of
the Bankruptcy Code in Case No. 99-21550 in the United States Bankruptcy Court
(herein called the "Court") for the Southern District of Texas (Corpus Christi
Division), entitled "In re: TransTexas Gas Corporation, et. al." (herein called
the "Bankruptcy Case");

         WHEREAS, pursuant to the Bankruptcy Case, the Court has issued an order
(herein called the "Bankruptcy Order") granting Seller's motion for permission
to (1) sell the Production Payment (as hereinafter defined) and enter into and
deliver to Grantee (as hereinafter defined) the Conveyance (as hereinafter
defined) and other ancillary marketing, transportation and processing agreements
and (2) amend or amend and restate and affirm certain existing marketing,
transportation and processing agreements with third parties in order to
relinquish certain of Seller's capacity under such existing marketing,
transportation and processing agreements as is required for Buyer to market,
transport and/or process the Production Payment hydrocarbons that Buyer and Fund
V (as hereinafter defined) and Fund VI (as hereinafter defined) own or control
and such other volumes of hydrocarbons as Buyer shall purchase from Seller or
other third parties;

         WHEREAS, pursuant to the Bankruptcy Order, Seller and Grantee have
entered into that certain Production Payment Conveyance (herein, as from time to
time amended, restated or otherwise modified, called the "Conveyance"), dated as
of March 14, 2000, from and by Seller, as grantor, and Buyer, TCW Portfolio No.
15555 DR V Sub-Custody Partnership, L.P. (herein called "Fund V") and TCW DR VI
Investment Partnership, L.P. (herein called "Fund VI") (in such capacity, Fund
VI together with Buyer and Fund V, collectively called the "Grantee"), whereby
Seller has granted, bargained, sold, conveyed, assigned, transferred, set over
and delivered to Grantee a term overriding royalty interest (herein called the
"Production Payment") in the Subject Interests (as defined in the Conveyance and
herein so called);

         WHEREAS, pursuant to the terms of the Conveyance, production from the
Subject Interests shall be dedicated to the Grantee as (1) at fifty percent
(50%) from March 1, 2000 until 9:00 a.m., Central Time, on September 1, 2000,
(2) at sixty-two percent (62%) from 9:00 a.m., Central Time, on September 1,
2000 until 9:00 a.m., Central Time, on March 1, 2001 and (3) seventy percent


<PAGE>   4


(70%) from and after 9:00 a.m., Central Time, on March 1, 2001 until the
Termination Time (herein called the "Dedication Percentage");

         WHEREAS, pursuant to the Bankruptcy Order, Seller and Grantee have
entered into that certain Purchase Agreement (herein, as from time to time
amended, restated, supplemented or otherwise modified, called the "Purchase
Agreement"), dated as of March 14, 2000, between Seller and Grantee and TCW
Asset Management Company, as agent on behalf of Fund V and Fund VI (herein
called the "Funds Agent"), whereby Seller has sold the first component of the
Production Payment to Grantee pursuant to the Conveyance, and Grantee has
purchased the same from Seller;

         WHEREAS, the Grantee and Buyer have entered into that certain
Production Sales Agreement (as defined in the Purchase Agreement and herein, as
from time to time amended, restated, supplemented or otherwise modified, called
the "Production Sales Agreement"), dated as of March 14, 2000, pursuant to which
Buyer has agreed to purchase, and Grantee has agreed to sell, Grantee's interest
in the Production Payment hydrocarbons; and

         WHEREAS, subject to the terms and conditions hereinafter set forth,
Buyer desires to purchase certain quantities of Gas from Seller and Seller
desires to sell such quantities of Gas to Buyer;

         NOW, THEREFORE, in consideration of the premises and of the mutual
covenants hereinafter set forth, the Parties hereto covenant and agree as
follows:


                                   ARTICLE I.
                             DEDICATION AND QUANTITY

         1.1 Subject to the other provisions of this Agreement, Seller does
hereby commit and dedicate to the performance of this Agreement and agrees to
sell and deliver to Buyer hereunder one hundred percent (100%) of the Gas
production which Seller owns, controls or has the right to sell, pursuant to the
Conveyance (as such Exhibit may from time to time be amended, restated,
supplemented, or otherwise modified) and that is capable of being transported to
Buyer's Purchaser under contracts with Buyer's Transporters (herein called the
"Marketed Volumes"). Seller represents and warrants that it has the right to
market and sell to Buyer hereunder the Marketed Volumes. Seller hereby agrees to
sell to Buyer, and Buyer hereby agrees to purchase from Seller, upon the terms
of this Agreement all of the Marketed Volumes which are actually delivered to
and accepted by Buyer's Purchaser.

         1.2 During the term hereof and as required by the applicable Buyer's
Marketing Agreements, Seller shall provide to Buyer, or to Buyer's designee, a
written nomination setting forth the quantity of Gas to be delivered to Buyer,
or to Buyer's designee, each Day during such Month (herein called the
"First-of-the-Month Nominated Quantity"). Seller shall provide to Buyer, or to
Buyer's designee, such notice as is required by the applicable Buyer's Marketing
Agreements prior to

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any Day for which Seller desires to nominate a quantity of Gas for sale and
delivery hereunder that is different from the First-of-the-Month Nominated
Quantity.

         1.3 In no event shall the volumes of Gas that Seller is obligated to
sell and deliver to Buyer, or to Buyer's designee, or that Buyer or Buyer's
designee have agreed to purchase and receive from Seller under the terms of this
Agreement ever exceed the volumes of Gas which can be legally produced or
purchased under the applicable rules and regulations of the Railroad Commission
of Texas.

         1.4 In consideration of the execution and delivery of this Agreement by
the Buyer, the Seller hereby indemnifies, exonerates and holds the Buyer and
each of its respective officers, directors, employees and agents (herein,
collectively, called the "Indemnified Parties") free and harmless from and
against any and all actions, causes of action, suits, losses, costs,
liabilities, damages and expenses (including, without limitation, reasonable
attorney's fees and disbursements) incurred in connection therewith
(irrespective of whether any such Indemnified Party is a Party to the action for
which indemnification hereunder is sought), excluding any portion of such
actions, causes of action, suits, losses, costs, liabilities, damages and
expenses (including, without limitation attorney's fees and disbursements)
resulting from the gross negligence or wilful misconduct of any Indemnified
Party (herein collectively called the "Indemnified Amounts"), incurred by the
Indemnified Parties or any of them as a result of, or arising out of, or
relating to (1) Buyer's Marketing Agreements or (2) this Agreement. IT IS
UNDERSTOOD BY THE PARTIES HERETO THAT THE INDEMNITIES BY SELLER IN FAVOR OF THE
BUYER IN THIS AGREEMENT SHALL BE APPLICABLE NOTWITHSTANDING THAT ANY INDEMNIFIED
AMOUNTS OTHERWISE COVERED BY THIS AGREEMENT ARE ATTRIBUTABLE TO THE NEGLIGENCE
(OTHER THAN GROSS NEGLIGENCE OR WILFUL MISCONDUCT) OF BUYER (WITHOUT REGARD TO
WHETHER SUCH NEGLIGENCE IS SOLE, JOINT, CONCURRENT, ACTIVE OR PASSIVE), ANY
PRE-EXISTING CONDITION OR DEFECT OR ANY FORM OF STRICT LIABILITY.

         1.5 In the event that Buyer incurs, owes or is liable for any
Indemnified Amount under Section 1.4 above, Seller shall pay such Indemnified
Amount by wire transfer of immediately available funds to Buyer within five (5)
days following Buyer's written demand therefor. In addition to, and not in
limitation of the foregoing, Buyer is hereby authorized at any time and from
time to time, without notice to Seller, to setoff and apply any and all sums
held and any other sums at any time owing to or for the credit or the account of
Seller against any and all sums owing to Buyer (including, without limitation,
reasonable attorney's fees and disbursements and any Indemnified Amount),
together with interest on such amounts at the Agreed Rate until paid in full,
irrespective of whether or not Buyer will have made any demand under this
Agreement. Buyer agrees promptly to notify Seller after any such setoff and
application. The rights of the Buyer under this Section 1.5 are in addition to
other rights and remedies (including, without limitation, other rights of
setoff) which Buyer may have. The provisions of Sections 1.4 and 1.5 shall
survive the termination of this Agreement.


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                                   ARTICLE II.
                      PRICE OF GAS AND NATURAL GAS LIQUIDS

         2.1 The Price per MMBtu of Gas on which the Net Price shall be
determined shall be the Price per MMBtu paid, calculated each Month by the
relevant Buyer's Purchaser for such Gas (excluding Products of Processing)
delivered hereunder during each applicable calendar Month from each field listed
in Exhibit B hereto. As described in Section VIII of Exhibit A, Buyer will pay
the Net Price to Seller for all Marketed Volumes (including Products of
Processing) delivered to Buyer and subsequently delivered to the relevant
Buyer's Purchaser and accepted and paid for by such Buyer's Purchaser hereunder.

         2.2 Notwithstanding anything contained in Paragraph 2.1 above to the
contrary, if deliveries of volumes of Gas from any of the fields listed on
Exhibit B give rise to an adjustment in Price under any Buyer's Marketing
Agreement, then the price for any such volumes of Gas delivered by Seller during
that month shall be a price per MMBtu equal to the applicable Price, with
adjustments thereto on account of such deliveries pursuant to the terms of the
applicable Buyer's Marketing Agreements for such Gas.

         2.3 If, during the term of this Agreement, the index or trade
publication cited in any Buyer's Sales Contract above ceases to exist or be
published, the provisions of such Buyer's Sales Contract with respect to a
replacement index or pricing mechanism for such Buyer's Sales Contract shall
apply in determining the Price for Gas from such field hereunder. Otherwise, the
Parties will endeavor to mutually agree to a replacement index or pricing
mechanism for Gas from such field. In the event the Parties cannot agree to a
replacement index or pricing mechanism for such Gas, then this Agreement shall
terminate with respect to the purchase of Gas from such field at the end of the
last Day for which an agreed upon price is applicable.

         2.4 Subject to the terms of Section VII of Exhibit A, Prices paid by
Buyer under this Article II are inclusive of severance tax reimbursement to
Buyer.

         2.5 The price payable for all volumes of Products of Processing which
are redelivered for the account of Buyer after processing by Buyer's Processor,
if any, shall be the Market Price per gallon then in effect for such Products of
Processing. Seller shall have the right to elect, from time to time on prior
written notice to Buyer and the relevant Buyer's Processor, to process or not
process Seller's Gas for the recovery of Products of Processing in accordance
with the terms and provisions of the respective Buyer's Processor's contract.


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<PAGE>   7


                                  ARTICLE III.
                          SELLER'S POINT(S) OF DELIVERY

         3.1 The points of delivery from Seller to Buyer for each field listed
on Exhibit B shall be the delivery point specified for such field as "Seller's
Delivery Point" on such Exhibit. In the event Seller delivers or causes to be
delivered Gas at any other delivery point, Buyer shall (to the extent it is
reasonably able to under the Buyer's Marketing Agreements) accept delivery
subject to a reduction in Net Price as provided in the definition of such term
to compensate Buyer for the reasonable charges, if any, resulting therefrom,
otherwise Buyer, or Buyer's designee, may elect not to accept delivery.

                                   ARTICLE IV.
                                      TERM

         4.1 Subject to the other provisions hereof, this Agreement shall be
effective with respect to production from and after 9 A.M. on March 1, 2000, and
shall remain in full force and effect for a primary term equal to the greater of
(a) three (3) years or (b) a period equal to the term of the Production Payment,
and Month to Month thereafter until terminated by either Party upon at least
thirty (30) Days' prior notice given in writing or by facsimile to the other
Party, which termination shall be effective on the first Day of the Month
following the expiration of such thirty (30) Day notice period; provided,
however, Buyer may terminate this Agreement, in full or in part, at any time
upon the giving of thirty (30) days notice of such termination to Seller, which
termination shall be effective as of the first Day of the Month following the
expiration of such thirty (30) Day notice period.

                                   ARTICLE V.
                                    NOTICES

         5.1 Any notice, request, demand, statement, payment or bill provided
for in this Agreement, or any notice which a Party may desire to give to the
other, shall be in writing and shall be considered as duly delivered as of the
date of transmittal if mailed by the U.S. Postal Service, telefaxed, wire or
courier expressed to the other Party at the following address:

BUYER:
         Notices & Correspondence:          Southern Producer Services, L.P.
                                            1200 Smith Street, Suite 2890
                                            Houston, Texas 77002
                                            Attention: David W. Stewart
                                            Phone:  (713) 276-1902
                                            Facsimile:  (713) 276-1990


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         Billing:                           Southern Producer Services, L.P.
                                            1200 Smith Street, Suite 2890
                                            Houston, Texas 77002
                                            Attention: Ron Franklin
                                            Phone:  (713) 276-1916
                                            Facsimile:  (713) 276-1990

SELLER:
         Notices & Correspondence:          TransTexas Gas Corporation
                                            1300 North Sam Houston Parkway East
                                            Suite 310
                                            Houston, Texas  77032-2949
                                            Attention:  Gas Marketing
                                            Phone:  (281) 987-8600
                                            Facsimile:  (281) 986-8840

         Payments By Wire Transfer:         TransTexas Gas Corporation
                                            Bank of New York
                                            48 Wall Street
                                            New York, New York
                                            ABA # 021-000-018
                                            For the Account of GMAC Commercial
                                            Credit LLC
                                            Acct. # 809-0653-114
                                            GAS - For further credit to
                                            account #904361
                                            CONDENSATE/LIQUIDS - For further
                                            credit to account #904200

         5.2 Either Party may change addresses by giving written notice to the
other Party.

                                   ARTICLE VI.
                                     GENERAL

         6.1 The GENERAL TERMS AND CONDITIONS attached hereto as Exhibit "A" are
incorporated herein as if set forth in full. In the event of any conflict
between the terms and conditions contained in this Agreement and the terms and
conditions contained in Exhibit "A", then the provisions contained in the body
of this Agreement shall prevail.

         6.2 ANY LITIGATION BASED HEREON, OR ARISING OUT OF, UNDER, OR IN
CONNECTION WITH, THIS AGREEMENT, OR ANY COURSE OF CONDUCT, COURSE OF DEALING,
STATEMENTS (WHETHER VERBAL OR WRITTEN) OR ACTIONS OF THE BUYER OR THE SELLER MAY
BE BROUGHT AND MAINTAINED IN THE COURTS OF THE STATE OF TEXAS OR IN THE UNITED
STATES DISTRICT COURT FOR THE SOUTHERN DISTRICT OF TEXAS; PROVIDED, HOWEVER,
THAT


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ANY SUIT SEEKING ENFORCEMENT AGAINST ANY PROPERTY MAY BE BROUGHT, AT THE BUYER'S
OPTION, IN THE COURTS OF ANY JURISDICTION WHERE SUCH PROPERTY MAY BE FOUND. THE
SELLER HEREBY EXPRESSLY AND IRREVOCABLY SUBMITS TO THE JURISDICTION OF THE
COURTS OF THE STATE OF TEXAS AND OF THE UNITED STATES DISTRICT COURT FOR THE
SOUTHERN DISTRICT OF TEXAS FOR THE PURPOSE OF ANY SUCH LITIGATION AS SET FORTH
ABOVE. THE SELLER FURTHER IRREVOCABLY CONSENTS TO THE SERVICE OF PROCESS BY
REGISTERED MAIL, POSTAGE PREPAID, OR BY PERSONAL SERVICE WITHIN OR WITHOUT THE
STATE OF TEXAS. THE SELLER HEREBY EXPRESSLY AND IRREVOCABLY WAIVES, TO THE
FULLEST EXTENT PERMITTED BY LAW, ANY OBJECTION WHICH IT MAY HAVE OR HEREAFTER
MAY HAVE TO THE LAYING OF VENUE OF ANY SUCH LITIGATION BROUGHT IN ANY SUCH COURT
REFERRED TO ABOVE AND ANY CLAIM THAT ANY SUCH LITIGATION HAS BEEN BROUGHT IN AN
INCONVENIENT FORUM. TO THE EXTENT THAT THE SELLER HAS OR HEREAFTER MAY ACQUIRE
ANY IMMUNITY FROM JURISDICTION OF ANY COURT OR FROM ANY LEGAL PROCESS (WHETHER
THROUGH SERVICE OR NOTICE, ATTACHMENT PRIOR TO JUDGMENT, ATTACHMENT IN AID OF
EXECUTION OR OTHERWISE) WITH RESPECT TO ITSELF OR ITS PROPERTY, THE SELLER
HEREBY IRREVOCABLY WAIVES SUCH IMMUNITY IN RESPECT OF ITS OBLIGATIONS UNDER THIS
AGREEMENT.

         6.3 SELLER AND BUYER HEREBY KNOWINGLY, VOLUNTARILY AND INTENTIONALLY
WAIVE THEIR RESPECTIVE RIGHTS TO A TRIAL BY JURY IN RESPECT OF ANY LITIGATION
BASED HEREON, OR ARISING OUT OF, UNDER, OR IN CONNECTION WITH, THIS AGREEMENT,
OR ANY COURSE OF CONDUCT, COURSE OF DEALING, STATEMENTS (WHETHER VERBAL OR
WRITTEN) OR ACTIONS OF THE BUYER, OR THE SELLER. EACH OF THE BUYER AND SELLER
ACKNOWLEDGES AND AGREES THAT IT HAS RECEIVED FULL AND SUFFICIENT CONSIDERATION
FOR THIS PROVISION AND THAT THIS PROVISION IS A MATERIAL INDUCEMENT FOR SUCH
PARTY'S ENTERING INTO THE PRODUCTION PAYMENT DOCUMENTS AND THIS AGREEMENT.

         6.4 This Agreement may be executed in any number of counterparts and by
different parties hereto on separate counterparts, each of which when so
executed and delivered shall be deemed to be an original, but all of which shall
taken together constitute one and the same instrument. Any signature delivered
by a party by facsimile transmission shall be deemed to be an original hereto.

                            [Signature pages follow]


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         IN WITNESS WHEREOF, the Parties hereto have caused this Agreement to be
executed in duplicate originals by their duly authorized officers effective as
of the Day and Year first hereinabove written.

SELLER:                                    BUYER:

TRANSTEXAS GAS CORPORATION                 SOUTHERN PRODUCER SERVICES, L.P.
                                           By: SC Ashwood Holdings, as its
                                               general partner


By:                                        By:
   ----------------------------------          ---------------------------------
Name:     Ed Donahue                       Name:     David W. Stewart
Title:    Vice President                   Title:    Vice President



ACKNOWLEDGED AND AGREED TO:

GMAC COMMERCIAL CREDIT LLC



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



                                      S-1