Document:

<PAGE>   1
                                                                   EXHIBIT 10.60

                         FIRST SUPPLEMENT TO PRODUCTION
                               PAYMENT CONVEYANCE

         THIS FIRST SUPPLEMENT TO PRODUCTION PAYMENT CONVEYANCE (this
"Supplement"), dated as of the date set out at the end hereof, is made by
TransTexas Gas Corporation, a Delaware corporation ("Grantor"), Southern
Producer Services, L.P. ("SPS"), TCW Portfolio No. 1555 DR V Sub-Custody
Partnership, L.P. ("Fund V"), and TCW DR VI Investment Partnership, L.P. ("Fund
VI"). SPS, Fund V and Fund VI are herein collectively called "Grantee".

                                    RECITALS:

A.   Effective as of March 1, 2000, Grantor executed in favor of Grantee that
     certain Production Payment Conveyance dated as of March 14, 2000 (as
     heretofore amended, the "Original Conveyance"), recorded as set forth in
     Schedule 1 hereto; all capitalized terms used but not defined herein shall
     have the meanings assigned to them in the Original Conveyance.

B.   Grantee and Grantor desire to supplement and amend the Original Conveyance
     in order to account for the payment by SPS of additional funds to Grantor.

C.   As described in Section 8.7 of the Original Conveyance, and pursuant to the
     Purchase Agreement referred to in the Original Conveyance, Fund V and Fund
     VI have appointed TCW Asset Management Company to act as their agent in
     connection with supplements and amendments to the Original Conveyance.

                           SUPPLEMENTS AND AGREEMENTS:

         FOR A GOOD AND VALUABLE CONSIDERATION, the receipt and sufficiency of
which are hereby acknowledged, Grantor and Grantee do hereby agree, act and
covenant as follows:

         1. Effective as of 9:00 a.m. Houston, Texas time, on June 7, 2000 (the
"Effective Time"), the Original Conveyance is amended in order to add the amount
of Eight Million Dollars ($8,000,000) to the unliquidated balance of the Primary
Sum, as such unliquidated balance stood as of the Effective Time after giving
effect to all applications of PP Proceeds made before the Effective Time. After
giving effect to such amendment (and to such application of PP Proceeds), the
unliquidated balance of the Primary Sum as of the Effective Time is $34,948,562.
(Any PP Proceeds received after the Effective Time on June 7, 2000 shall be
deemed to have been received on the next following Business Day.)

         2. All of the terms and provisions of the Original Conveyance, as the
same is amended and supplemented hereby, are ratified, adopted, affirmed and
renewed, and remain in full force

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and effect for the benefit of Grantee, the Beneficiaries, Funds Agent, and their
respective successors and assigns.

         3. The definition of "Percentage Share" in Section 1.1 of the Original
Conveyance is hereby amended in its entirety to read as follows:

                  " 'Percentage Share' means, with respect to each Person
         included in Grantee, the fractional undivided interest which it owns in
         the Production Payment at the time in question. From the initial grant
         of the Production Payment until 9:00 a.m. Houston, Texas time, on June
         7, 2000, the Percentage Share of each Person included in Grantee was as
         follows:

                  Fund V   42.859594%
                  Fund VI  21.429797%
                  SPS      35.710609%

         From and after 9:00 a.m. Houston, Texas time, on June 7, 2000, the
         Percentage Share of each Person included in Grantee is as follows:

                  Fund V   33.048697%
                  Fund VI  16.524349%
                  SPS      50.426954%"

The foregoing Percentage Shares of Fund V, Fund VI and SPS, respectively, are in
this Amendment called their "amended Percentage Shares".

         4. In consideration of the additional purchase price payment made by
SPS to Grantor and the foregoing increase in the unliquidated balance of the
Primary Sum:

                  (a) Fund V and Fund VI do hereby GRANT, BARGAIN, SELL, CONVEY,
         ASSIGN, TRANSFER, SET OVER and DELIVER unto SPS such additional
         undivided interests in the Production Payment as are necessary in order
         to cause SPS, Fund V and Fund VI to own the Production Payment, at and
         after the Effective Time, in undivided interests in proportion to their
         respective amended Percentage Shares, and

                  (b) Fund V and Fund VI do further assign unto SPS such
         undivided interests in Fund V's and Fund VI's accounts receivable from
         the sale of PP Hydrocarbons -- to the extent such accounts receivable
         exist and are unpaid at the Effective Time and arise from the sale of
         PP Hydrocarbons before the Effective Time -- as are necessary in order
         to cause SPS, Fund V and Fund VI to share in all collections of such
         accounts receivable after the Effective Time in proportion to their
         respective amended Percentage Shares.

         TO HAVE AND TO HOLD the same, upon and subject to the terms of the
Original Conveyance, as amended hereby, unto SPS and its successors and
Permitted Assigns, until the Termination Time.

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         5. This Supplement may be executed in multiple counterparts, all of
which are identical.

         6. This Supplement shall be binding upon and shall inure to the benefit
of the parties hereto, and their respective successors and assigns, and all of
the covenants and agreements contained in the Original Conveyance, as amended
hereby, shall be deemed to be covenants and agreements running with the lands
affected thereby.

         7. This Supplement shall be governed by and construed in accordance
with the laws of the State of Texas, without regard to principles of conflicts
of laws.

         IN WITNESS WHEREOF, this Supplement is executed by the parties hereto
on the dates set out below in their respective acknowledgments, but effective as
of the Effective Time.

                                       TRANSTEXAS GAS CORPORATION

                                       By:  /s/ ED DONAHUE
                                           ------------------------------------
                                           Ed Donahue
                                           Vice President

Grantor's address:                     1300 North Sam Houston Parkway East
                                       Suite 310
                                       Houston, Texas 77032-2949
                                       Attention: Ed Donahue, Vice President
                                       Telephone: 281/987-8600
                                       Telecopy:  281/986-8865

                                       SOUTHERN PRODUCER SERVICES, L.P.

                                       By:  SC Ashwood Holdings, Inc.,
                                            its general partner

                                            By:  /s/ DAVID W. STEWART
                                               --------------------------------
                                               David W. Stewart
                                               Vice President

SPS's address:                         1200 Smith Street
                                       Suite 2890
                                       Houston, Texas 77002
                                       Attention: David W. Stewart
                                       Telephone: 713/276-1902
                                       Telecopy:  713/276-1990

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<PAGE>   4

                                    TCW PORTFOLIO NO. 1555 DR V SUB-CUSTODY
                                    PARTNERSHIP, L.P., and
                                    TCW DR VI INVESTMENT PARTNERSHIP, L.P.

                                    By: TCW ASSET MANAGEMENT COMPANY, as
                                        Agent

                                        By:  /s/ KURT A. TALBOT
                                            -----------------------------------
                                            Kurt A. Talbot
                                            Senior Vice President

Fund V's and Fund VI's address:     c/o Trust Company of the West
                                    865 South Figueroa
                                    Los Angeles, California  90017
                                    Attention: Thomas F. Mehlberg
                                    Telephone: 213/244-0702
                                    Telecopy:  213/244-0604

This document prepared by:

John W. Rain
Thompson & Knight L.L.P.
1700 Pacific Avenue, Suite 3300
Dallas, Texas  75201

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<PAGE>   5

STATE OF TEXAS      )
                    )
COUNTY OF HARRIS    )

        The foregoing instrument was acknowledged before me on this 7th day of
June, 2000, by Ed Donahue, the Vice President of TransTexas Gas Corporation, a
Delaware corporation, on behalf of such corporation.

                                        /s/ GLENDA J. BUSH
                                       ----------------------------------------
        [SEAL]                         Notary Public, State of Texas

STATE OF TEXAS       )
                     )
COUNTY OF HARRIS     )

         The foregoing instrument was acknowledged before me on this 7th day of
June, 2000, by David W. Stewart, the Vice President of SC Ashwood Holdings,
Inc., a Georgia corporation, on behalf of such corporation acting as general
partner of Southern Producer Services L.P., a Delaware limited partnership, and
on behalf of such limited partnership.

                                        /s/ GLENDA J. BUSH
                                       ----------------------------------------
         [SEAL]                        Notary Public, State of Texas

STATE OF TEXAS        )
                      )
COUNTY OF HARRIS      )

         The foregoing instrument was acknowledged before me on this 7th day of
June, 2000, by Kurt A. Talbot, the Senior Vice President of TCW Asset Management
Company, a California corporation, on behalf of such corporation acting as agent
as aforesaid.

                                        /s/ GLENDA J. BUSH
                                       ----------------------------------------
         [SEAL]                        Notary Public, State of Texas

                                        5

<PAGE>   6

                                                                      SCHEDULE 1

                               RECORDING SCHEDULE

1.       Production Payment Conveyance among TCW Portfolio No. 1555 DR V
         Sub-Custody Partnership, L.P., TCW DR VI Investment Partnership, L.P.,
         Southern Producer Services, L.P. and TransTexas Gas Corporation.

         Recording Jurisdiction                        Recording Data
         ----------------------                        --------------

         Chambers County, TX                           Document No. 00-448-604,
                                                       Filed 3/17/2000

         Galveston County, TX                          Film Code #014-39-1028,
                                                       Filed 3/17/2000

         Jim Hogg County, TX                           Volume 17, Page 362,
                                                       Filed 3/20/2000

         Live Oak County, TX                           Volume 449, Page 135,
                                                       Filed 3/20/2000

         Wharton County, TX                            Volume 360, Page 596,
                                                       Filed 3/17/2000

         Zapata County, TX                             Volume 629, Page 471,
                                                       Filed 3/17/2000

         General Land Office of Texas                  Sent for filing

                                        6<PAGE>   1
                                                                   EXHIBIT 10.61

                     SECOND SUPPLEMENT TO PURCHASE AGREEMENT

         THIS SECOND SUPPLEMENT TO PURCHASE AGREEMENT dated as of September 8,
2000 (this "Supplement"), is made by:

         o        TransTexas Gas Corporation, a Delaware corporation (herein
                  called "Grantor"),

         o        Southern Producer Services, L.P. ("SPS"),

         o        TCW Portfolio No. 1555 DR V Sub-Custody Partnership, L.P.
                  ("Fund V") and TCW DR VI Investment Partnership, L.P. ("Fund
                  VI"), acting through their agent, TCW Asset Management
                  Company, and

         o        TCW Asset Management Company, as Agent on behalf of Fund V and
                  Fund VI (in such capacity, "Funds Agent").

                                    RECITALS

         1. Grantor, SPS, Fund V, Fund VI and Funds Agent have heretofore
entered into that certain Purchase Agreement dated as of March 14, 2000 (herein,
as heretofore amended or supplemented, called the "Original Purchase
Agreement"), and, as contemplated therein, Grantor has, by means of a Production
Payment Conveyance dated as of the same date (herein, as heretofore amended or
supplemented, called the "Original Conveyance"), conveyed to SPS, Fund V and
Fund VI (collectively, "Grantee") the "Production Payment" as therein defined,
burdening interests of Grantor in certain oil and gas properties.

         2. As contemplated in the Original Purchase Agreement, Grantor now
desires to supplement and amend the Original Conveyance in consideration of the
payment by SPS of an additional Purchase Price Payment, as more fully described
below.

         3. Section 2.3(b) of the Original Purchase Agreement provides that
Grantor can offer to make additional Production Units subject to the Production
Payment in consideration of the payment by SPS of an additional Purchase Price
Payment to Grantor.

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants and agreements contained herein, Grantor, SPS, Fund V, Fund VI, and
Funds Agent hereby agree as follows:

                     ARTICLE I - Definitions and References

         Section 1.1. Defined Terms and References. As used herein, the terms
"Original Conveyance", "Original Purchase Agreement", "Grantor", "SPS", "Fund
V", "Fund VI", "Grantee" and "Funds Agent" have the meanings given them above.
Reference is also made to the Original Purchase Agreement and to the Original
Conveyance for the meaning of various terms defined therein, all of which shall
when used herein (unless otherwise expressly defined herein)

<PAGE>   2

have the same meanings. For purposes of this Supplement, unless the context
otherwise requires, the following additional terms shall have the following
meanings:

         "Current Closing Date" has the meaning given such term in Section 2.3.

         "Current Conveyance Supplement" means the Second Supplement to
Production Payment Conveyance executed by Grantor and Grantee substantially in
the form of Exhibit A hereto.

         "Current Purchase Price Payment" means a Purchase Price Payment in the
amount of $10,000,000.

         "Current Supplement Documents" means this Supplement, the Current
Conveyance Supplement, and all other Production Payment Documents delivered
substantially contemporaneously herewith.

         "Production Payment Conveyance" means the Original Conveyance as
amended and supplemented by the Current Conveyance Supplement.

         "Purchase Agreement" means the Original Purchase Agreement as
supplemented and amended hereby.

         Section 1.2. Rules of Construction. All references in this Supplement
to articles, sections, subsections and other subdivisions refer to corresponding
articles, sections, subsections and other subdivisions of this Supplement unless
expressly provided otherwise. Titles appearing at the beginning of any of such
subdivisions are for convenience only and shall not constitute part of such
subdivisions and shall be disregarded in construing the language contained in
such subdivisions. The words "this Supplement, "this instrument", "herein",
"hereof", "hereby", "hereunder" and words of similar import refer to this
Supplement as a whole and not to any particular subdivision unless expressly so
limited. Unless the context otherwise requires: "including" (and its grammatical
variations) means "including without limitation"; "or" is not exclusive; words
in the singular form shall be construed to include the plural and vice versa;
words in any gender include all other genders; references herein to any
instrument or agreement refer to such instrument or agreement as it may be from
time to time supplemented or amended; and references herein to any Person
include such Person's successors and assigns. All references in this Supplement
to exhibits and schedules refer to the exhibits and schedules to this Supplement
unless expressly provided otherwise, and all such exhibits and schedules are
hereby incorporated herein by reference and made a part hereof for all purposes.

                             ARTICLE II - Amendment

         Section 2.1. Agreement to Amend. Upon the terms and conditions of this
Supplement and the Purchase Agreement, Grantor and Grantee agree to amend and
supplement the Original Conveyance by executing and delivering the Current
Conveyance Supplement.

         Section 2.2. Closing. On the Current Closing Date, Grantor shall
deliver the Current Supplement Documents to Grantee, Grantor shall satisfy all
of the conditions set out in

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<PAGE>   3

Sections 3.4 and 3.5 of the Purchase Agreement, and the following additional
condition shall be satisfied:

         o        Grantor shall provide Grantee with subordination instruments,
                  in form and substance satisfactory to Grantee, from any
                  Persons holding liens or security interests on the properties
                  described in the Current Conveyance Supplement.

Thereupon, SPS shall pay all of the Current Purchase Price Payment to Grantor in
accordance with the terms and procedures of the Purchase Agreement.

         Section 2.3. Time and Place of Closing. The closing for the
consummation of the transactions contemplated herein shall take place on
September 8, 2000 or on such other date as may be agreed to by Grantor and
Grantee (herein called the "Current Closing Date").

         Section 2.4. Waiver of Conditions. Section 3.4 of the Original Purchase
Agreement specifies various conditions for the payment of the Current Purchase
Price Payment. Grantee hereby waives, with respect to the Current Purchase Price
Payment only, the conditions set out in subsections (b), (d), (e), (f), (g) and
(k) of Section 3.4 of the Original Purchase Agreement.

         Section 2.5. Waiver of Covenant. Pursuant to the Current Conveyance
Supplement, the "Additional Subject Interests" (as defined therein and herein so
called) are being made subject to the Production Payment Conveyance. Section
3.2(a)(ii) of the Production Payment Conveyance allows Grantor to abandon any
Subject Well (along with the associated Subject Interests) if, after it has
become a Commercial Well, it then ceases to be a Commercial Well. Grantee hereby
agrees, in connection with the Additional Subject Interests only, that Grantor
may abandon any such Additional Subject Interest if there is no Commercial Well
located thereon, regardless of whether any Subject Well located thereon had ever
become a Commercial Well.

                   ARTICLE III - Representations and Covenants

         Section 3.1. Representations and Warranties of Grantor. To induce
Grantee to enter into the Current Supplement Documents and to pay the Current
Purchase Price Payment, Grantor hereby represents and warrants and covenants to
Grantee that:

         (a) All representations and warranties made by Grantor or any other
TransTexas Company in any Production Payment Document now or previously
delivered are true and correct as of the Current Closing Date (unless such
representations and warranties are expressly limited to an earlier date, in
which case such representations and warranties are true and correct as of such
earlier date). Without limitation of the foregoing, no Senior Notes Event of
Default exists.

         (b) Each TransTexas Company has performed all agreements, covenants,
and conditions which it is required by any Production Payment Document to
perform on or prior to the Current Closing Date.

         (c) The consummation on the Current Closing Date of the transactions
contemplated in the Current Supplement Documents: (i) is not prohibited by any
law or any regulation or order

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<PAGE>   4

of any court or governmental agency or authority applicable to Grantor or any
other TransTexas Company, and (ii) does not subject any of them to any penalty
or other onerous condition under or pursuant to any such law, regulation or
order.

         (d) Grantor has paid in full in cash all costs associated with drilling
(including completing or plugging and abandoning) each well located on any
"Additional Subject Lands" as defined in the Current Conveyance Supplement. Upon
production in paying quantities from such Additional Subject Lands, Grantor will
enter into appropriate amendments to the TransTexas Marketing Agreements and
such related documentation as Marketer reasonable requests.

         Section 3.2. Covenants. To induce Grantee to enter into the Current
Supplement Documents and to pay the Current Purchase Price Payment, Grantor
hereby covenants with Grantee that Grantor will perform all of its covenants and
duties under the Production Payment Documents, all as fully as if they were set
out in full herein.

         Section 3.3. Representations and Warranties of Grantee. Each Person
included within Grantee hereby represents and warrants to Grantor that: (a) such
Person has incurred no obligation or liability, contingent or otherwise, for
broker's or finder's fees in respect of any of the matters provided for in this
Supplement for which fees Grantor might be liable; (b) the Purchase Agreement
constitutes the legal, valid and binding act and obligation of such Person,
enforceable against such Person in accordance with its terms except as such
enforcement may be limited by bankruptcy, insolvency, moratorium and other
similar laws applicable to creditors' rights generally or by general principles
of equity; (c) no bankruptcy or insolvency proceeding is presently pending (or,
to such Person's best knowledge, threatened) by or against such Person under any
applicable bankruptcy, insolvency or other similar law of any jurisdiction; (d)
such Person has not made a general assignment for the benefit of creditors; (e)
such Person is acquiring the Production Payment for its own account and not with
any intention to transfer all or any part of the Production Payment to others in
violation of the Securities Act of 1933, as amended, or any other applicable
securities laws, and (f) such Person is a "United States person", within the
meaning of Section 7701 of the Internal Revenue Code of 1986, as amended. Fund V
and Fund VI further represent and warrant that in connection with the
transactions contemplated herein and in the Purchase Agreement (i) they are
represented by Funds Agent, an investment manager that qualifies as a "qualified
professional asset manager" as defined in Department of Labor Prohibited
Transaction Exemption 84-14 (the "QPAM Exemption") and (ii) each of the
conditions of the QPAM Exemption are satisfied and will, throughout the term of
the Purchase Agreement (as hereby supplemented and amended), be satisfied.

                           ARTICLE IV - Miscellaneous

         Section 4.1. Ratification of Production Payment Documents. The Original
Purchase Agreement as hereby supplemented and amended is hereby ratified and
confirmed in all respects. The other Production Payments Documents, as they may
be supplemented, amended or affected by the Current Supplement Documents, are
hereby ratified and confirmed in all respects. Any reference to the Purchase
Agreement in any Production Payment Document shall be deemed to refer to this
Supplement also, and any reference in any Production Payment Document to any
other document or instrument amended, renewed, extended or otherwise affected by
any Current

                                        4

<PAGE>   5

Supplement Document shall also refer to such Current Supplement Document. The
execution, delivery and effectiveness of this Supplement and the other Current
Supplement Documents shall not, except as expressly provided herein or therein,
operate as a waiver of any right, power or remedy of Grantee or Funds Agent
under the Purchase Agreement or any other Production Payment Document nor
constitute a waiver of any provision of the Purchase Agreement or any other
Production Payment Document.

         Section 4.2. Survival of Agreements. All representations, warranties,
covenants and agreements of Grantor herein shall survive the execution and
delivery of this Supplement and the other Current Supplement Documents and shall
further survive until terminated in accordance with the Purchase Agreement.

         Section 4.3. Production Payment Documents. This Supplement and the
other Current Supplement Documents are Production Payment Documents, and all
provisions in the Purchase Agreement pertaining to Production Payment Documents
(including the arbitration provisions of Section 6.9 of the Purchase Agreement)
apply hereto and thereto.

         THIS WRITTEN AGREEMENT AND THE OTHER PRODUCTION PAYMENT DOCUMENTS
REPRESENT THE FINAL AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY
EVIDENCE OF PRIOR, CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS OF THE
PARTIES.

         THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

         Section 4.4. Governing Law. This Supplement shall be deemed a contract
and instrument made under the laws of the State of Texas and shall be construed
and enforced in accordance with and governed by the laws of the State of Texas
and the laws of the United States of America, without regard to principles of
conflicts of law.

         Section 4.5. Counterparts. This Supplement may be separately executed
in counterparts and by the different parties hereto in separate counterparts,
each of which when so executed shall be deemed to constitute one and the same
Supplement.

            [THE REMAINDER OF THIS PAGE IS INTENTIONALLY LEFT BLANK]

                                        5

<PAGE>   6

         IN WITNESS WHEREOF, this Supplement is executed as of the date first
written above.

                                      TRANSTEXAS GAS CORPORATION

                                      By:   /s/ ED DONAHUE
                                           -------------------------------------
                                           Ed Donahue
                                           Vice President

                                      SOUTHERN PRODUCER SERVICES, L.P.

                                      BY:  SC Ashwood Holdings, Inc.,
                                           its general partner

                                           By:  /s/ DAVID W. STEWART
                                               ---------------------------------
                                               David W. Stewart
                                               Vice President

                                      TCW PORTFOLIO NO. 1555 DR V SUB-CUSTODY
                                      PARTNERSHIP, L.P. and
                                      TCW DR VI INVESTMENT PARTNERSHIP, L.P.

                                      By:  TCW ASSET MANAGEMENT COMPANY, as
                                           their Agent

                                           By:  /s/ KURT A. TALBOT
                                               ---------------------------------
                                               Kurt A. Talbot
                                               Senior Vice President

                                      TCW ASSET MANAGEMENT COMPANY, as Agent

                                      By: /s/ KURT A. TALBOT
                                         ---------------------------------------
                                         Kurt A. Talbot
                                         Senior Vice President

                                        6

<PAGE>   7

                                 ACKNOWLEDGMENT

         To induce Grantee to enter into the above Supplement, the undersigned
Galveston Bay Pipeline Company and Galveston Bay Processing Company each hereby
ratify and confirm their various agreements made in connection with the
Production Payment Documents referred to above and acknowledge and agree that
such agreements remain in full force and effect after taking into account the
Current Supplement Documents referred to above.

EXECUTED as of September 8, 2000.

GALVESTON BAY PIPELINE COMPANY

By:     /s/ ED DONAHUE
       --------------------------------
       Name:  Ed Donahue
       Title: Vice President

GALVESTON BAY PROCESSING COMPANY

By:     /s/ ED DONAHUE
       --------------------------------
       Name:  Ed Donahue
       Title: Vice President

                                        7

<PAGE>   8

                                                                       EXHIBIT A

                          CURRENT CONVEYANCE SUPPLEMENT

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