<PAGE>

                                                                    EXHIBIT 10.1

                               FIFTH AMENDMENT TO
                           REVOLVING CREDIT AGREEMENT

     THIS FIFTH AMENDMENT TO REVOLVING CREDIT AGREEMENT (the "Amendment") is
made and entered into as of the 30th day of April, 2003 (the "Effective Date"),
by and among XTO ENERGY INC. (successor by name change to Cross Timbers Oil
Company), a Delaware corporation ("Company"), the Banks that are signatories
hereto (collectively, the "Banks"), JP MORGAN CHASE BANK (successor by merger to
Morgan Guaranty Trust Company of New York), as Administrative Agent for Banks,
BANK OF AMERICA, N.A., as Syndication Agent for Banks, JP MORGAN CHASE BANK
(successor by merger to The Chase Manhattan Bank), as Documentation Agent for
Banks, and FLEET NATIONAL BANK, as Co-Documentation Agent for Banks.

                              W I T N E S S E T H:

     WHEREAS, Company, JPMorgan Chase Bank (successor by merger to Morgan
Guaranty Trust Company of New York), as Administrative Agent for Banks, Bank of
America N.A., as Syndication Agent for Banks, JPMorgan Chase Bank (successor by
merger to The Chase Manhattan Bank), as Documentation Agent for Banks, Fleet
National Bank, as Co-Documentation Agent for Banks, and Banks have entered into
that certain Revolving Credit Agreement dated as of May 12, 2000 (as amended by
that certain First Amendment to Revolving Credit Agreement dated as of June 20,
2000 among Company and Banks, as amended by that certain Second Amendment to
Revolving Credit Agreement dated as of February 16, 2001 among Company and
Banks, as amended by that certain Third Amendment to Revolving Credit Agreement
dated as of May 1, 2001 among Company and Banks, as amended by that certain
Fourth Amendment to Revolving Credit Agreement dated as of May 3, 2002 among
Company and Banks as amended hereby and as amended from time to time hereafter,
the "Loan Agreement").

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

     NOW, THEREFORE, in consideration of the premises herein contained and other
good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties, intending to be legally bound, agree as follows:

                                    ARTICLE I
                           Definitions and References

     1.01 Unless otherwise specifically defined herein, each term used herein
which is defined in the Loan Agreement as in effect immediately prior to the
Effective Date shall have the meaning assigned to such term in the Loan
Agreement as so in effect. Each reference to "hereof," "hereunder," "herein" and
"hereby" and each other similar reference and each reference to "this Loan
Agreement" and each other similar reference contained in the Loan

<PAGE>

Agreement shall from and after the Effective Date refer to the Loan Agreement as
amended hereby.

                                   ARTICLE II
                                   Amendments

     2.01. Amendment to Article I; Additional Defined Terms. Effective as of the
Effective Date, Article I of the Loan Agreement is amended by including the
following defined terms:

          ""Investment Grade Rating" shall mean a rating equal to or higher than
     Baa3 (or the equivalent) by Moody's or BBB- (or the equivalent) by S&P."

          ""Moody's" shall mean Moody's Investors Service, Inc. and its
     successors."

          ""Qualifying Rating" shall mean (a) an Investment Grade Rating from
     both Rating Agencies or (b) an Investment Grade Rating from either Rating
     Agency and a rating from the other Rating Agency that is the rating
     immediately below the Investment Grade Rating for such Rating Agency (being
     Ba1 (or the equivalent) by Moody's or BB+ (or the equivalent) by S&P."

          ""Rating Agencies" shall mean each of S&P and Moody's."

          ""S&P" shall mean Standard and Poor's Corporation and its successors."

     2.02. Amendment to Section 3.08. Effective as of the Effective Date,
Article 3 of the Loan Agreement is amended by including the following Section
3.08 at the conclusion of such Article:

          "3.08. Release of Liens." At such time that Company's senior unsecured
     long-term Indebtedness receives a Qualifying Rating and (i) there exists no
     Event of Default or event which with notice or lapse of time or both would
     constitute an Event of Default and/or (ii) there exists no Borrowing Base
     Deficiency, Administrative Agent, upon written request of Company while
     such Qualifying Rating is in effect, shall (without vote or consent of any
     Bank) take such actions as shall be required to release the Lien in all
     Mineral Properties, HGT Units, ART Units, the Capital Stock of the
     Subsidiaries and other assets or properties that serve as collateral for
     the Loan and shall return the Letters in Lieu to Company. Upon the release
     of such Liens, (i) the defined terms "Collateral Documents," "Letters in
     Lieu," and "Mortgaged Properties" as set forth in Article I of this Loan
     Agreement shall be deleted and references to such defined terms as they
     appear throughout this Loan Agreement shall be deleted and (ii) Article 3
     (excepting Section 3.07 and this Section 3.08) and Sections 8.19, 8.20,
     8.21 and 10.01(p) of this Agreement shall no longer be applicable and shall
     be deemed deleted from this Loan Agreement."

                                       2

<PAGE>

     2.03. Amendment to Section 8.22. Effective as of the Effective Date,
Section 8.22 of the Loan Agreement is amended by including the following phrase
following the phrase "at the Closing Date and" in the fifth (5th) line of such
Section:

          ", unless Section 3.08 of this Loan Agreement has been given effect
     prior to the creation of such Subsidiary,"

     2.04. Amendment to Article 8. Effective as of the Effective Date, Article 8
of the Loan Agreement is amended by including the following Section 8.25 at the
conclusion of such Article:

          "8.25 Reportable Transactions. Company does not intend to treat the
     Advances and related transactions as being a "reportable transaction"
     (within the meaning of Treasury Regulation Section 1.6011-4). In the event
     Company determines to take any action inconsistent with such intention, it
     will promptly notify the Administrative Agent thereof."

     2.05. Amendment to Section 13.19. Effective as of the Effective Date,
Section 13.19 of the Loan Agreement is amended by including the following
sentence at the conclusion of such Section:

     "Notwithstanding anything herein to the contrary, "confidential
     information" shall not include, and each Bank may disclose without
     limitation of any kind, any information with respect to the "tax treatment"
     and "tax structure" (in each case, within the meaning of Treasury
     Regulation Section 1.6011-4) of the transactions contemplated hereby and
     all materials of any kind (including opinions or other tax analysis) that
     are provided to such Bank relating to such tax treatment and tax structure;
     provided that with respect to any document or similar item that in either
     case contains information concerning the tax treatment or tax structure of
     the transaction as well as other information, this sentence shall only
     apply to such portions of the document or similar item that relate to the
     tax treatment or tax structure of the Advances and transactions
     contemplated hereby."

     2.06. Amendment to Section 13.20. Effective as of the Effective Date,
Section 13.20 of the Loan Agreement is amended by including the following
sub-clause (c) at the conclusion of such Section:

          "(c) If Company should exercise its rights under Section 3.08 of this
     Loan Agreement and all conditions set forth in such Section 3.08 to the
     exercise of such rights have been satisfied, Administrative Agent shall
     (without notice to or vote or consent of any Bank) take such actions as
     shall be required to release the Lien in all Mineral Properties, HGT Units,
     ART Units and other assets or properties that serve as collateral for the
     Loan, and to return the Letters in Lieu to Company."

                                       3

<PAGE>

     2.07. Amendment to Schedule I. Effective as of the Effective Date, Schedule
I to the Loan Agreement is deleted and the Schedule I attached hereto is
substituted therefor.

                                   ARTICLE III
                          Borrowing Base Determination

     3.01. Pursuant to Section 5.03 of the Loan Agreement, effective as of the
Effective Date, the Borrowing Base is $1,827,000,000. Company and Banks agree
that such Borrowing Base shall be effective as of the Effective Date (rather
than the June 30, 2003 Determination Date, it being agreed that the Borrowing
Base will not be subject to an additional redetermination of June 30, 2003) and
shall remain in effect until it is subsequently redetermined pursuant to Section
5.03 (for the Determination Date of June 30, 2004) or 5.04 of the Loan Agreement
or is adjusted according to Section 5.05 of the Loan Agreement.

                                   ARTICLE IV
                               Condition Precedent

     4.01. Counterparts; Conditions to Effectiveness. This instrument shall
become effective (and the Loan Agreement shall be amended with the amendments
referred to herein) as of the Effective Date when Administrative Agent shall
have received a duly executed counterpart hereof signed by Company and all Banks
(or, in the case of any Bank as to which an executed counterpart shall not have
been received, Administrative Agent shall have received telegraphic, telex or
other written confirmation from such party of execution of a counterpart hereof
by such Bank).

     4.02. Amendment Fee. Upon Administrative Agent's receipt of duly executed
counterparts hereof signed by Company and all Banks, Company shall pay to
Administrative Agent (for the account of all Banks) a fee in the amount of 12.5
bps (basis points) of the Commitment, and Administrative Agent shall distribute
to each Bank such Bank's Percentage of such fee. The fee payable under this
Section 3.02 shall be paid by Company to Administrative Agent within three (3)
Business Days after Company's receipt of Administrative Agent's written request
or invoice for same.

                                    ARTICLE V
                  Ratifications, Representations and Warranties

     5.01. Ratifications. The terms and provisions set forth herein shall modify
and supersede all inconsistent terms and provisions set forth in the Loan
Agreement immediately before giving effect hereto and the other Loan Papers,
and, except as expressly modified, amended, and superseded herein, the terms and
provisions of the Loan Agreement and the other Loan Papers are ratified and
confirmed and shall continue in full force and effect. Company and Banks agree
that the Loan Agreement, as amended hereby, and the other Loan Papers shall
continue to be legal, valid, binding and enforceable in accordance with their
respective terms.

                                       4

<PAGE>

     5.02. Representations, Warranties and Agreements. Company hereby represents
and warrants to Banks that (a) the execution, delivery and performance of the
Loan Agreement as amended hereby has been authorized by all requisite corporate
action on the part of Company and will not violate the Articles/Certificate of
Incorporation or Bylaws of Company; (b) the representations and warranties
contained in the Loan Agreement, as amended hereby, and any other Loan Papers
are true and correct on and as of the date hereof and on and as of the date of
execution hereof as though made on and as of each such date; (c) no Default or
Event of Default under the Loan Agreement, as amended hereby, has occurred and
is continuing; and (d) Company is in full compliance with all covenants and
agreements contained in the Loan Agreement and the other Loan Papers, as amended
hereby.

                                   ARTICLE VI
                           Ratifications by Guarantors

     6.01. Ratification by Guarantors. CT Trading and the Gas Marketing
Subsidiaries (collectively, the "Guarantors") hereby acknowledge and agree to
the terms hereof and hereby ratify and reaffirm all of their respective
obligations under their unconditional guaranties of the Loan and Obligation (the
"Guaranties"). Guarantors also hereby agree that nothing in this Amendment shall
adversely affect any right or remedy of Banks under the Guaranties and that the
execution and delivery of this Amendment shall in no way change or modify their
respective obligations as guarantor under the Guaranties. Although the
Guarantors have been informed by Company of the matters set forth in this
Amendment and the Guarantors have acknowledged and agreed to the same, the
Guarantors understand that Banks have no duty to notify Guarantors or to seek
Guarantors' acknowledgment or agreement, and nothing contained herein shall
create such a duty as to any transaction hereafter.

                                   ARTICLE VII
                            Miscellaneous Provisions

     7.01. Reference to Loan Agreement. The other Loan Papers, and any and all
other agreements, documents or instruments now or hereafter executed and
delivered pursuant to the terms hereof or pursuant to the terms of the Loan
Agreement, as amended hereby, are hereby amended so that any reference in the
Loan Agreement and such other Loan Papers to the Loan Agreement shall mean a
reference to the Loan Agreement as amended hereby.

     7.02. Expenses of Agents. As provided in the Loan Agreement, Company agrees
to pay on demand all reasonable costs and expenses incurred by Agents in
connection with the preparation, negotiation and execution of this Amendment,
including, without limitation, the costs and fees of Agent's legal counsel, and
all reasonable costs and expenses incurred by Banks in connection with the
enforcement or preservation of any rights under the Loan Agreement, as amended
hereby, or any other Loan Papers, including, without, limitation, the reasonable
costs and fees of Agents' legal counsel. Company shall not be responsible for
the cost or expense of legal counsel of any other Bank in connection with the
preparation, execution and delivery of this Amendment.

                                       5

<PAGE>

     7.03. Counterparts. This instrument may be executed in one or more
counterparts, each of which when so executed shall be deemed to be an original,
but all of which when taken together shall constitute one and the same
instrument.

     7.04. Headings. The headings, captions, and arrangements used herein are
for convenience only and shall not affect the interpretation of this instrument.

     7.05. Applicable Law. THE LOAN AGREEMENT AS AMENDED HEREBY AND ALL OTHER
LOAN PAPERS EXECUTED PURSUANT HERETO SHALL BE DEEMED TO HAVE BEEN MADE AND TO BE
PERFORMABLE IN AND SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE
LAWS OF THE STATE OF TEXAS UNLESS THE LAWS GOVERNING NATIONAL BANKS SHALL HAVE
APPLICATION.

     7.06. Final Agreement. THE LOAN AGREEMENT AS AMENDED HEREBY AND THE OTHER
LOAN PAPERS, EACH AS AMENDED HEREBY, REPRESENT THE ENTIRE EXPRESSION OF THE
PARTIES WITH RESPECT TO THE SUBJECT MATTER HEREOF ON THE EFFECTIVE DATE THIS
AMENDMENT IS EXECUTED. THE LOAN AGREEMENT AS AMENDED HEREBY AND THE OTHER LOAN
PAPERS, AS AMENDED HEREBY, 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. NO MODIFICATION, RESCISSION,
WAIVER, RELEASE OR AMENDMENT OF ANY PROVISION OF THE LOAN AGREEMENT OR THE OTHER
LOANS PAPERS SHALL BE MADE, EXCEPT BY A WRITTEN AGREEMENT SIGNED BY COMPANY AND
EITHER BANKS OR MAJORITY BANKS, AS PROVIDED IN THE LOAN AGREEMENT.

     IN WITNESS WHEREOF, this Amendment has been executed in multiple originals
and is effective as of the date first above-written.

                           [SIGNATURE PAGES TO FOLLOW]

                                       6

<PAGE>

                                        COMPANY:

                                        XTO ENERGY COMPANY, INC.,
                                        a Delaware corporation

                                        By:          /s/ JOHN O'REAR
                                            ------------------------------------
                                            John O'Rear, Vice President and
                                              Treasurer

                                        GUARANTORS:

                                        CROSS TIMBERS TRADING COMPANY,
                                        a Texas corporation

                                        By:          /s/ JOHN O'REAR
                                            ------------------------------------
                                            John O'Rear, Vice President and
                                              Treasurer

                                        RINGWOOD GATHERING COMPANY,
                                        a Delaware corporation

                                        By:          /s/ LOUIS G. BALDWIN
                                            ------------------------------------
                                            Louis G. Baldwin, Vice President
                                              and Treasurer

                                        CROSS TIMBERS ENERGY SERVICES, INC.,
                                        a Texas corporation,

                                        By:          /s/ LOUIS G. BALDWIN
                                            ------------------------------------
                                            Louis G. Baldwin, Vice President
                                              and Treasurer

                                        TIMBERLAND GATHERING & PROCESSING
                                          COMPANY, INC., a Texas corporation

                                        By:          /s/ LOUIS G. BALDWIN
                                            ------------------------------------
                                            Louis G. Baldwin, Vice President
                                              and Treasurer

                                       7

<PAGE>

                                        BANKS:

                                        JP MORGAN CHASE BANK

                                        By:          /s/ ROBERT C. MERTENSOTTO
                                            ------------------------------------
                                            Robert C. Mertensotto, Managing
                                              Director

                                        BANK OF AMERICA, N.A.

                                        By:          /s/ RICHARD STEIN
                                            ------------------------------------
                                            Richard Stein, Managing Director

                                        FLEET NATIONAL BANK

                                        By:       /s/ JEFFREY H. RATHKAMP
                                            ------------------------------------
                                            Name:    Jeffrey H. Rathkamp
                                                 -------------------------------
                                            Title:   Vice President
                                                  ------------------------------

                                        ABN-AMRO BANK N.V., HOUSTON AGENCY

                                        By:      ABN-AMRO NORTH AMERICA, INC.

                                        By:          /s/ STUART MURRAY
                                            ------------------------------------
                                            Name:    Stuart Murray
                                                 -------------------------------
                                            Title:   Group Vice President
                                                  ------------------------------

                                        By:          /s/ JOHN REED
                                            ------------------------------------
                                            Name:    John Reed
                                                 -------------------------------
                                            Title:   Vice President
                                                  ------------------------------

                                        BANK ONE, NA

                                        By:          /s/ J. Scott Fowler
                                            ------------------------------------
                                            J. Scott Fowler, Director, Capital
                                              Markets

                                       8

<PAGE>

                                        BNP PARIBAS

                                        By:          /s/ BETSY JOCHER
                                            ------------------------------------
                                            Name:    Betsy Jocher
                                                 -------------------------------
                                            Title:   Vice President
                                                  ------------------------------

                                        By:          /s/ GABE ELLISOR
                                            ------------------------------------
                                            Name:    Gabe Ellisor
                                                 -------------------------------
                                            Title:   Vice President
                                                  ------------------------------


                                        WACHOVIA BANK,  NATIONAL ASSOCIATION

                                        By:      /s/ DAVID E. HUMPHREYS
                                            ------------------------------------
                                        Name:    David E. Humphreys
                                             -----------------------------------
                                        Title:   Vice President
                                              ----------------------------------

                                        BANK OF MONTREAL

                                        By:          /s/ JAMES V. DUCOTE
                                            ------------------------------------
                                            Name:    James V. Ducote
                                                 -------------------------------
                                            Title:   Director
                                                  ------------------------------

                                        THE BANK OF NEW YORK

                                        By:          /s/ RAYMOND J. PALMER
                                            ------------------------------------
                                            Name:    Raymond J. Palmer
                                                 -------------------------------
                                            Title:   Vice President
                                                  ------------------------------

                                        THE BANK OF NOVA SCOTIA

                                        By:          /s/ N. BELL
                                            ------------------------------------
                                            Name:    N. Bell
                                                 -------------------------------
                                            Title:   Senior Manager Loan
                                                       Operations
                                                  ------------------------------

                                        BANK OF SCOTLAND

                                        By:         /s/ JOSEPH FRATUS
                                            ------------------------------------
                                            Name:    Joseph Fratus
                                                 -------------------------------
                                            Title:   First Vice President
                                                  ------------------------------

                                       9

<PAGE>

                                        COMERICA BANK-TEXAS

                                        By:          /s/ MICHELE L. JONES
                                            ------------------------------------
                                        Name:    Michele L. Jones
                                             -----------------------------------
                                        Title:   Vice President
                                              ----------------------------------


                                        CREDIT LYONNAIS NEW YORK BRANCH

                                        By:        /s/ OLIVIER AUDEMARD
                                            ------------------------------------
                                        Name:    Olivier Audemard
                                             -----------------------------------
                                        Title:   Senior Vice President
                                              ----------------------------------
                                        Document:  XTO ENERGY INC FIFTH
                                                 -------------------------------
                                        AMENDMENT TO REVOLVING CREDIT
                                        ----------------------------------------
                                        AGREEMENT
                                        ----------------------------------------

                                        FORTIS CAPITAL CORP.

                                        By:          /s/ DEIDRE SANBORN
                                            ------------------------------------
                                        Name:    Deidre Sanborn
                                             -----------------------------------
                                        Title:   Vice President
                                              ----------------------------------

                                        By:       /s/ DARRELL W. HOLLEY
                                            ------------------------------------
                                        Name:    Darrell W. Holley
                                             -----------------------------------
                                        Title:   Managing Director
                                              ----------------------------------


                                        NATEXIS BANQUES POPULAIRES

                                        By:        /s/ PHILIPPE ROBIN
                                            ------------------------------------
                                        Name:    Philippe Robin
                                             -----------------------------------
                                        Title:   Senior Vice President
                                              ----------------------------------

                                        By:         /s/ DANIEL PAYER
                                            ------------------------------------
                                        Name:    Daniel Payer
                                             -----------------------------------
                                        Title:   Vice President
                                              ----------------------------------

                                        U.S. BANK NATIONAL ASSOCIATION

                                        By:               /s/ MARK E. THOMPSON
                                            ------------------------------------
                                            Mark E. Thompson, Vice President

                                       10

<PAGE>
                                        WELLS FARGO BANK (TEXAS), N.A.

                                        By:        /s/ CHARLES D. KIRKHAM
                                            ------------------------------------
                                            Charles D. Kirkham, Vice President

                                        CITIBANK USA, INC.

                                        By:      /s/ DOUGLAS WHIDDON
                                            ------------------------------------
                                        Name:    Douglas Whiddon
                                             -----------------------------------
                                        Title:   Attorney-In-Fact
                                              ----------------------------------


                                        MIZUHO CORPORATE BANK, LTD.

                                        By:      /s/ THOMAS W. BOYLAN
                                            ------------------------------------
                                        Name:    Thomas W. Boylan
                                             -----------------------------------
                                        Title:   Vice President
                                              ----------------------------------


                                        WASHINGTON MUTUAL BANK

                                        By:      /s/ MARK ISENSEE
                                            ------------------------------------
                                        Name:    Mark Isensee
                                             -----------------------------------
                                        Title:   Vice President
                                              ----------------------------------


                                        UFJ BANK LIMITED

                                        By:        /s/ CLYDE L. REDFORD
                                            ------------------------------------
                                        Name:    Clyde L. Redford
                                             -----------------------------------
                                        Title:   Senior Vice President
                                              ----------------------------------


                                        THE FROST NATIONAL BANK

                                        By:          /s/ JOHN S. WARREN
                                            ------------------------------------
                                            John S. Warren, Senior Vice
                                              President


                                       11

<PAGE>

                                   SCHEDULE I

                                                                 Share of
Bank                                          Percentage         Commitment
----                                          ----------         ----------
JPMORGAN CHASE BANK                             8.7500%          $70,000,000
BANK OF AMERICA, N.A.                           8.1250%          $65,000,000
FLEET NATIONAL BANK                             6.2500%          $50,000,000
CREDIT LYONNAIS NEW YORK BRANCH                 5.9375%          $47,500,000
ABN AMRO BANK, N.V.                             5.0000%          $40,000,000
BANK ONE, NA                                    5.0000%          $40,000,000
BNP PARIBAS                                     5.0000%          $40,000,000
WACHOVIA BANK, NATIONAL ASSOCIATION             5.0000%          $40,000,000
BANK OF MONTREAL                                4.0625%          $32,500,000
BANK OF NEW YORK                                4.0625%          $32,500,000
THE BANK OF NOVA SCOTIA                         4.0625%          $32,500,000
BANK OF SCOTLAND                                4.0625%          $32,500,000
COMERICA BANK-TEXAS                             4.0625%          $32,500,000
FORTIS CAPITAL CORP.                            4.0625%          $32,500,000
NATEXIS BANQUE BFCE                             4.0625%          $32,500,000
U.S. BANK NATIONAL ASSOCIATION                  4.0625%          $32,500,000
WELLS FARGO BANK (TEXAS), N.A.                  4.0625%          $32,500,000
CITICORP NORTH AMERICA, INC.                    3.1250%          $25,000,000
MIZUHO CORPORATE BANK, LTD.                     3.1250%          $25,000,000
UFJ BANK LIMITED                                3.1250%          $25,000,000
WASHINGTON MUTUAL BANK                          3.1250%          $25,000,000
THE FROST NATIONAL BANK                         1.8750%          $15,000,000
                                                ------            ----------
                  Total                         100.00%         $800,000,000

                                       12