<PAGE>
                                                                 EXHIBIT 10.8(j)


                       SIXTH AMENDMENT TO CREDIT AGREEMENT


         This SIXTH AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is entered
into effective as of June 29, 2001, among WOODWARD MARKETING, L.L.C., a Delaware
limited liability company (the "Borrower"), BANK OF AMERICA, N. A. ("Bank of
America"), as a Bank, as an Issuing Bank, and as Agent for the Banks, BNP
PARIBAS, a bank organized under the laws of France ("BNP Paribas"), and Atmos
Energy Marketing LLC (the "Guarantor").

         WHEREAS, Borrower and Banks entered into that certain Credit Agreement,
dated to be effective as of August 9, 2000, as amended by that certain First
Amendment to Credit Agreement and Guaranty of Atmos Energy Marketing, LLC dated
as of September 29, 2000, that certain Second Amendment to Credit Agreement
dated as of November 3, 2000, that certain Third Amendment to Credit Agreement
dated as of December 5, 2000, that certain Fourth Amendment to Credit Agreement
dated as of December 22, 2000, and that certain Fifth Amendment to Credit
Agreement dated as of December 31, 2000 (as amended the "Credit Agreement"); and

         WHEREAS, all Obligations (as defined in the Credit Agreement) are
guaranteed by the Guarantor pursuant to a Second Amended And Restated Guaranty
of Atmos Energy Marketing, LLC executed by the Guarantor, in favor of the Banks
(the "Guaranty Agreement"); and

         WHEREAS, the Obligations are secured by security interests in the
Collateral (as defined in the Credit Agreement) granted to Agent for the benefit
of the Banks pursuant to the Security Agreements (as defined in the Credit
Agreement) and pursuant to the Nations Funds Security Agreement (as defined in
the Credit Agreement), each executed by Borrower (collectively, the "Security
Agreements"); and

         WHEREAS, the parties hereto desire to amend the Credit Agreement as set
forth herein.

         NOW, THEREFORE, in consideration of the mutual covenants and agreements
herein contained, Borrower, Bank of America, BNP Paribas and the Guarantor agree
as follows:

         1.       The definition of "Expiration Date" set forth in Section 1.01
of the Credit Agreement is deleted in its entirety and replaced with the
following definition:

                  "Expiration Date" means the earliest to occur of:

                           (a)      September 30, 2001; or

                           (b)      the date demand for payment is made by the
                                    Agents; or

                           (c)      the date an Event of Default occurs.


SIXTH AMENDMENT TO CREDIT AGREEMENT - Page 1


<PAGE>


         2.       The definition of "Maturity Date" set forth in Section 1.01 of
the Credit Agreement is deleted in its entirety and replaced with the following
definition:

                  "Maturity Date" means December 31, 2001.

         3.       Renewal; Continued Effect. Except as set forth above, the
Credit Agreement shall continue in full force and effect.

         4.       Representations. To induce the Agent and the Banks to enter
into this Amendment, Borrower ratifies and confirms each representation and
warranty set forth in the Credit Agreement as if such representations and
warranties were made on even date herewith, and further represents and warrants
(a) that no material adverse change has occurred in the financial condition or
business prospects of Borrower since the date of the last financial statements
delivered to the Banks, (b) that no Event of Default exists and no event or
condition exists or has occurred which with passage of time, or notice, or both,
would become an Event of Default (a "Default"), and (c) that Borrower is fully
authorized to enter into this Amendment. BORROWER ACKNOWLEDGES THAT THE CREDIT
AGREEMENT PROVIDES FOR A CREDIT FACILITY THAT IS COMPLETELY OPTIONAL ON THE PART
OF THE BANKS AND THAT THE BANKS HAVE ABSOLUTELY NO DUTY OR OBLIGATION TO ADVANCE
ANY REVOLVING LOAN OR TO ISSUE ANY LETTER OF CREDIT. BORROWER REPRESENTS AND
WARRANTS TO THE BANKS THAT BORROWER IS AWARE OF THE RISKS ASSOCIATED WITH
CONDUCTING BUSINESS UTILIZING AN UNCOMMITTED FACILITY.

         5.       Conditions Precedent. As a condition to Agent and the Banks
entering into this Amendment, no Default or Event of Default shall exist on the
date hereof, and Agent and the Banks must have received executed originals of
each of the following documents and instruments, in form and substance
satisfactory to Agent and the Banks:

                  (a)      this Amendment, duly executed by Borrower; and

                  (b)      such other documents or certificates as Agent may
                           reasonably request.

         6.       Ratification of Security Agreements. Borrower ratifies and
confirms the Security Agreements, and acknowledges and agrees that references to
the Credit Agreement in such Security Agreements are hereby amended to refer to
the Credit Agreement as amended by this Amendment and that in all other respects
such Security Agreements shall continue in full force and effect, and that
pursuant to such Security Agreements Borrower has granted and hereby confirms
and grants to Agent for the benefit of the Banks a continuing first and prior
security interest in the Collateral to secure payment and performance of all
Obligations.

         7.       Guaranty Ratification. Atmos Energy Marketing, LLC ratifies
and confirms the SECOND AMENDED AND RESTATED GUARANTY OF ATMOS ENERGY MARKETING,
LLC and acknowledges and agrees that such Guaranty Agreement shall continue in
full force and


SIXTH AMENDMENT TO CREDIT AGREEMENT - Page 2


<PAGE>


effect, and that pursuant to the Guaranty Agreement, the Guarantor has
guaranteed and continues to guaranty the full payment and performance of all
Obligations under the Credit Agreement, as amended from time to time.

         8.       Notes Amendment and Ratification. The Borrower ratifies and
confirms the Promissory Notes issued to Bank of America and BNP Paribas and
acknowledges and agrees that such Promissory Notes shall continue in full force
and effect, and shall be "Notes" as defined in the Credit Agreement, as amended
hereby.

         9.       Miscellaneous.

                  (a) Severability. In case any of the provisions of this
Amendment shall for any reason be held to be invalid, illegal, or unenforceable,
such invalidity, illegality, or unenforceability shall not affect any other
provision hereof, and this Amendment shall be construed as if such invalid,
illegal, or unenforceable provision had never been contained herein.

                  (b) Capitalized Terms. Except as otherwise defined herein,
capitalized terms shall have the meanings specified in the Credit Agreement.

                  (c) Execution in Counterparts. This Amendment may be executed
in any number of counterparts, all of which taken together shall constitute one
and the same instrument, and any party hereto may execute this Amendment by
signing one or more counterparts.

                  (d) Governing Law. This Amendment shall be construed in
accordance with and governed by the laws of the State of California (without
reference to principles of conflicts of laws), provided, however, that Agent,
Banks and all Agent-Related Persons shall retain all rights under federal law.

                  (e) Rights of Third Parties. All provisions herein are imposed
solely and exclusively for the benefit of Borrower, Agent, Banks and all
Agent-Related Persons, and their permitted successors and assigns, and no other
Person shall be a direct or indirect legal beneficiary of, or have any direct or
indirect cause of action or claim in connection with this Amendment or any of
the other Loan Documents.

                  (f) COMPLETE AGREEMENT. THIS WRITTEN AMENDMENT AND THE OTHER
WRITTEN AGREEMENTS ENTERED INTO AMONG THE PARTIES REPRESENT THE FINAL AGREEMENT
AMONG 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 AMONG THE PARTIES.


SIXTH AMENDMENT TO CREDIT AGREEMENT - Page 3


<PAGE>


               Executed as of the day and year first above written



                                            BORROWER:


                                            WOODWARD MARKETING, L.L.C.,
                                            a Delaware limited liability company



                                            By:     /s/ J. D. WOODWARD
                                               ---------------------------------
                                            Name:   J. D. Woodward
                                                 -------------------------------
                                            Title:  President
                                                  ------------------------------


                                            BANKS:


                                            BANK OF AMERICA, N. A.,
                                            as Agent


                                            By:     /s/ IRENE C. RUMMEL
                                               ---------------------------------
                                            Name:   Irene C. Rummel
                                                 -------------------------------
                                            Title:  Principal
                                                  ------------------------------


SIXTH AMENDMENT TO CREDIT AGREEMENT - Page 4


<PAGE>


                                            BANK OF AMERICA, N. A.,
                                            as a Bank and Issuing Bank


                                            By:     /s/ IRENE C. RUMMEL
                                               ---------------------------------
                                            Name:   Irene C. Rummel
                                                 -------------------------------
                                            Title:  Principal
                                                  ------------------------------

                                            BNP PARIBAS,
                                            as a Bank


                                            By:     /s/ EDWARD K. CHIN
                                               ---------------------------------
                                            Name:   Edward K. Chin
                                                 -------------------------------
                                            Title:  Director
                                                  ------------------------------


                                            By:     /s/ KEITH COX
                                               ---------------------------------
                                            Name:   Keith Cox
                                                 -------------------------------
                                            Title:  Director
                                                  ------------------------------


SIXTH AMENDMENT TO CREDIT AGREEMENT - Page 5


<PAGE>


                                            GUARANTOR:



                                            ATMOS ENERGY MARKETING, LLC


                                            By:     /s/ LAURIE M. SHERWOOD
                                               ---------------------------------
                                            Name:   Laurie M. Sherwood
                                                 -------------------------------
                                            Title:  Vice President and Treasurer
                                                  ------------------------------




SIXTH AMENDMENT TO CREDIT AGREEMENT - Page 6