Document:

<PAGE>

                                                                    EXHIBIT 4.18

                      FOURTH AMENDMENT TO CREDIT AGREEMENT

         THIS FOURTH AMENDMENT TO CREDIT AGREEMENT (this "Fourth Amendment"),
dated as of March 7, 2003, is entered into among ELKCORP (formerly known as
Elcor Corporation), a Delaware corporation (the "Borrower"), the lenders listed
on the signature pages hereof as Lenders (the "Lenders"), BANK ONE, N.A., as
Documentation Agent, and BANK OF AMERICA, N.A., as Administrative Agent, Swing
Line Lender and L/C Issuer.

                                   BACKGROUND

         A.       The Borrower, certain of the Lenders, the Documentation Agent,
the Syndication Agent, the Administrative Agent, the Swing Line lender and the
L/C Issuer are parties to that certain Credit Agreement, dated as of November
30, 2000, as amended by that certain First Amendment to Credit Agreement, dated
as of March 31, 2001, that certain Second Amendment to Credit Agreement, dated
as of June 5, 2002, and that certain Third Amendment to Credit Agreement, dated
as of February 20, 2003 (said Credit Agreement, as amended, the "Credit
Agreement"). The terms defined in the Credit Agreement and not otherwise defined
herein shall be used herein as defined in the Credit Agreement.

         B.       The Borrower has requested (a) certain amendments to the
Credit Agreement, (b) to add Hibernia National Bank ("Hibernia"), Washington
Mutual Bank, FA ("Washington Mutual") and Branch Banking and Trust Company
("BBT") (collectively, "New Lenders") and (c) to remove The Frost National Bank
("Frost") and Wachovia Bank, N.A. ("Wachovia") (collectively, "Exiting Lenders")
as lenders under the Credit Agreement.

         C.       The Lenders, the Documentation Agent, the Administrative
Agent, the Swing Line Lender and the L/C Issuer hereby agree to amend the Credit
Agreement, subject to the terms and conditions set forth herein.

         NOW, THEREFORE, in consideration of the covenants, conditions and
agreements hereafter set forth, and for other good and valuable consideration,
the receipt and adequacy of which are all hereby acknowledged, the Borrower, the
Lenders, the Swing Line Lender, the L/C Issuer and the Administrative Agent
covenant and agree as follows:

         1.       AMENDMENTS.

         (a)      The definition of "Applicable Rate" set forth in Section 1.01
of the Credit Agreement is hereby amended to read as follows:

                  "Applicable Rate" means the following percentages per annum:

<TABLE>
<CAPTION>
---------------------------------------------------------------------------------------------
PRICING                                     COMMITMENT          EURODOLLAR RATE
 LEVEL            LEVERAGE RATIO               FEE              LETTERS OF CREDIT   BASE RATE
---------------------------------------------------------------------------------------------
<S>         <C>                             <C>                 <C>                 <C>
  VI        Greater than or equal to
            3.50 to 1                          0.625                3.000             1.500
---------------------------------------------------------------------------------------------
  V         Greater than or equal to           0.500                2.375             0.875
---------------------------------------------------------------------------------------------
</TABLE>

                                       1
<PAGE>

<TABLE>
<CAPTION>
---------------------------------------------------------------------------------------------
PRICING                                     COMMITMENT          EURODOLLAR RATE
 LEVEL            LEVERAGE RATIO               FEE              LETTERS OF CREDIT   BASE RATE
---------------------------------------------------------------------------------------------
<S>         <C>                             <C>                 <C>                 <C>
            3.00 to 1 but less than
            3.50 to 1
---------------------------------------------------------------------------------------------
  IV        Greater than or equal to
            2.50 to 1 but less than
            3.00 to 1                          0.375                1.875             0.375
---------------------------------------------------------------------------------------------
  III       Greater than or equal to
            2.00 to 1 but less than
            2.50 to 1                          0.375                1.375             0.000
---------------------------------------------------------------------------------------------
  II        Greater than or equal to
            1.50 to 1 but less than
            2.00 to 1                          0.250                1.125             0.000
---------------------------------------------------------------------------------------------
  I         Less than 1.50 to 1                0.250                1.000             0.000
---------------------------------------------------------------------------------------------
</TABLE>

                  The Applicable Rate shall be adjusted on each Adjustment Date
         as tested by using the Leverage Ratio set forth on the Compliance
         Certificate on each Adjustment Date. If the financial statements
         required pursuant to Section 6.01 and the related Compliance
         Certificate required pursuant to Section 6.02(b) are not received by
         the Administrative Agent by the date required, the Applicable Rate
         shall be determined using Pricing Level VI until such time as such
         financial statements and Compliance Certificate are received.

         (b)      The definition of "Fixed Charge Coverage Ratio" set forth in
Section 1.01 of the Credit Agreement is hereby amended to read as follows:

                  "Fixed Charge Coverage Ratio" means, as of any date of
         determination, the ratio of (a) the remainder of (i) Consolidated
         EBITDA for the period of four consecutive fiscal quarters ending on
         such date, minus (ii) Cash Taxes for the period of four consecutive
         fiscal quarters ending on such date, minus (iii) Maintenance Capital
         Expenditures to (b) the sum of (i) Consolidated Interest Expense for
         the period of four consecutive fiscal quarters ending on such date,
         plus (ii) principal payments of Indebtedness of the Borrower and its
         Subsidiaries required to be paid during the period of four consecutive
         fiscal quarters ending on such date.

         (c)      Section 1.01 of the Credit Agreement is hereby amended by
adding the defined term "Maintenance Capital Expenditures" thereto to read as
follows:

                  "Maintenance Capital Expenditures" means an amount equal to
                  $12,000,000.

         (d)      Section 1.01 of the Credit Agreement is hereby amended by
deleting the defined terms "Consolidated Interest Charges" and "Private
Placement Debt" therefrom.

         (e)      Section 7.09 of the Credit Agreement is hereby amended to read
as follows:

                                       2
<PAGE>

                  7.09 BURDENSOME AGREEMENTS. Enter into any Contractual
         Obligation that limits the ability of any Subsidiary to make Restricted
         Payments to the Borrower or to otherwise transfer property to the
         Borrower.

         (f)      Section 2.14(a) of the Credit Agreement is hereby amended by
amending the first sentence thereof to read as follows:

                  Upon notice to the Administrative Agent (which shall promptly
         notify the Lenders), the Borrower may from time to time, request an
         increase in the Aggregate Commitments by up to $50,000,000.

         (g)      Section 7.12 of the Credit Agreement is hereby amended to read
as follows:

                  7.12     FINANCIAL COVENANTS.

                  (a)      Consolidated Net Worth. Permit Consolidated Net Worth
         as of the end of any fiscal quarter of the Borrower to be less than the
         sum of (i) $130,000,000, (ii) an amount equal to 50% of the
         Consolidated Net Income earned in each fiscal year ending after June
         30, 2001 (with no deduction for a net loss in any such fiscal year) and
         (iii) an amount equal to 100% of the aggregate increases in
         Shareholders' Equity of the Borrower and its Subsidiaries after the
         date hereof by reason of the issuance and sale of Capital Stock of the
         Borrower (including upon any conversion of debt securities of the
         Borrower into such Capital Stock, but excluding any sales of treasury
         stock), or the conversion or exchange of preferred Capital Stock of the
         Borrower into common Capital Stock of the Borrower.

                  (b)      Fixed Charge Coverage Ratio. Permit the Fixed Charge
         Coverage Ratio to be less than either (i) 1.75 to 1 as of the end of
         more than two consecutive fiscal quarters or (ii) 1.50 to 1 as of the
         end of any fiscal quarter.

                  (c)      Capitalization Ratio. Permit the Capitalization Ratio
         to be greater than 0.55 to 1 at the end of any fiscal quarter.

         (h)      Schedule 2.01 is hereby amended to be in the form of Schedule
2.01 to this Fourth Amendment, and the Commitment of each Lender , after giving
effect to this Fourth Amendment, is set forth on such Schedule 2.01.

         (i)      Exhibit E to the Credit Agreement is hereby amended to be in
the form of Exhibit E to this Fourth Amendment.

         2.       REPRESENTATIONS AND WARRANTIES TRUE; NO EVENT OF DEFAULT. By
its execution and delivery hereof, the Borrower represents and warrants that, as
of the date hereof:

         (a)      the representations and warranties contained in the Credit
Agreement and the other Loan Documents are true and correct on and as of the
date hereof as made on and as of such date;

                                       3
<PAGE>

         (b)      no event has occurred and is continuing which constitutes a
Default or an Event of Default;

         (c)      (i) the Borrower has full power and authority to execute and
deliver this Fourth Amendment, the Revolving Loan Note payable to the order of
each New Lender (collectively, the "New Notes"), the replacement Revolving Loan
Note payable to the order of each Lender whose Commitment has been amended
pursuant to this Fourth Amendment (collectively, the "Replacement Notes"), (ii)
this Fourth Amendment, the New Notes and the Replacement Notes have been duly
executed and delivered by the Borrower, and (iii) this Fourth Amendment, the New
Notes and the Replacement Notes and the Credit Agreement, as amended hereby,
constitute the legal, valid and binding obligations of the Borrower, enforceable
in accordance with their respective terms, except as enforceability may be
limited by applicable debtor relief laws and by general principles of equity
(regardless of whether enforcement is sought in a proceeding in equity or at
law) and except as rights to indemnity may be limited by federal or state
securities laws;

         (d)      neither the execution, delivery and performance of this Fourth
Amendment, the New Notes, the Replacement Notes or the Credit Agreement, as
amended hereby, nor the consummation of any transactions contemplated herein or
therein, will conflict with any Law or Organization Documents of the Borrower,
or any indenture, agreement or other instrument to which the Borrower or any of
its property is subject; and

         (e)      no authorization, approval, consent, or other action by,
notice to, or filing with, any governmental authority or other Person not
previously obtained is required for the execution, delivery or performance by
the Borrower of this Fourth Amendment, the New Notes or the Replacement Notes.

         3.       CONDITIONS TO EFFECTIVENESS. This Fourth Amendment shall be
effective (and the revisions to the definition of "Applicable Rate" set forth in
Section 1(a) hereof will go into effect) upon satisfaction or completion of the
following:

         (a)      the Administrative Agent shall have received counterparts of
this Fourth Amendment executed by the Required Lenders;

         (b)      the Administrative Agent shall have received counterparts of
this Fourth Amendment executed by the Borrower and acknowledged by each
Guarantor;

         (c)      the Administrative Agent shall have received a certified
resolution of the Board of Directors of the Borrower authorizing the execution,
delivery and performance of this Fourth Amendment, the New Notes and the
Replacement Notes;

         (d)      the Administrative Agent shall have received an opinion of
counsel to the Borrower, in form and substance satisfactory to the
Administrative Agent, with respect to matters set forth in Sections 2(c), (d)
and (e) of this Fourth Amendment;

                                       4
<PAGE>

         (e)      the Administrative Agent shall have received a duly executed
(i) New Note for each New Lender and (ii) Replacement Note for each Lender whose
Commitment is being amended by this Fourth Amendment;

         (f)      Frost and Wachovia shall each have received payment in full of
all amounts due and owing to them under the Credit Agreement; and

         (g)      the Administrative Agent shall have received, in form and
substance satisfactory to the Administrative Agent and its counsel, such other
documents, certificates and instruments as the Administrative Agent shall
require.

         4.       PURCHASE BY LENDERS. Simultaneously with the satisfaction of
conditions of effectiveness set forth in Section 3 hereof, each Lender shall
purchase or sell (as the case may be), without recourse, an amount of Loans and
L/C Obligations outstanding such that after giving effect to this Fourth
Amendment, the amount of each Lender's Commitment under the Credit Agreement
which has been utilized shall be pro rata among the Lenders in the proportion
that their respective Commitments bear to the Aggregate Commitment. The parties
hereto agree that the provisions of Section 10.07 of the Credit Agreement shall
not be applicable to the addition of the New Lenders pursuant to this Fourth
Amendment. Each New Lender represents and warrants to the Administrative Agent
as follows:

         (a)      such New Lender has received a copy of the Credit Agreement
and all amendments thereto, together with copies of the most recent financial
statements of the Borrower delivered pursuant thereto, and it is an Eligible
Assignee;

         (b)      it has the full power and authority and the legal right to
make, deliver and perform, and has taken all necessary action, to authorize the
execution, delivery and performance of this Fourth Amendment, and any and all
other documents delivered by it in connection herewith and to fulfill its
obligations under, and to consummate the transactions contemplated by, this
Fourth Amendment and the other Loan Documents, and no consent or authorization
of, filing with, or other act by or in respect of any Governmental Authority, is
required in connection herewith or therewith;

         (c)      under applicable Laws no tax will be required to be withheld
by the Administrative Agent or the Borrower with respect to any payments to be
made to such New Lender under any Loan Document, and no tax forms described in
Section 10.15 of the Credit Agreement are required to be delivered by such New
Lender; and

         (d)      such New Lender has received and reviewed such other documents
and information as it has deemed appropriate to make its own credit analysis and
decision to enter into this Fourth Amendment and become a party to the Credit
Agreement. Such New Lender has independently and without reliance upon the
Administrative Agent or any other Person, and based on such information as such
New Lender has deemed appropriate, made its own credit analysis and decision to
enter into this Fourth Amendment and become a party to the Credit Agreement.
Such New Lender will, independently and without reliance upon the Administrative
Agent or any other Lender, and based upon such documents and information as it
shall deem

                                       5
<PAGE>

appropriate at the time, continue to make its own credit decisions in taking or
not taking action under the Credit Agreement.

         5.       EXITING LENDERS. Upon satisfaction of the conditions set forth
in Section 3 of this Fourth Amendment, (a) no Exiting Lender shall (i) be a
Lender under the Credit Agreement or (ii) have any rights or obligations with
respect to being a Lender, except for those that expressly survive termination
of the Credit Agreement or termination of any commitments thereunder and (b)
each Exiting Lender shall mark its Revolving Loan Note "PAID IN FULL", and
promptly return its Revolving Loan Note to the Borrower.

         6.       REFERENCE TO THE CREDIT AGREEMENT.

         (a)      Upon the effectiveness of this Fourth Amendment, each
reference in the Credit Agreement to "this Agreement", "hereunder", or words of
like import shall mean and be a reference to the Credit Agreement, as affected
and amended hereby.

         (b)      The Credit Agreement, as amended by the amendments referred to
above, shall remain in full force and effect and is hereby ratified and
confirmed.

         7.       COSTS, EXPENSES AND TAXES. The Borrower agrees to pay on
demand all costs and expenses of the Administrative Agent in connection with the
preparation, reproduction, execution and delivery of this Fourth Amendment and
the other instruments and documents to be delivered hereunder (including the
reasonable fees and out-of-pocket expenses of counsel for the Administrative
Agent with respect thereto).

         8.       GUARANTOR'S ACKNOWLEDGMENT. By signing below, each Guarantor
(a) acknowledges, consents and agrees to the execution, delivery and performance
by the Borrower of this Fourth Amendment, (b) acknowledges and agrees that its
obligations in respect of its Guaranty (i) are not released, diminished, waived,
modified, impaired or affected in any manner by this Fourth Amendment or any of
the provisions contemplated herein, (c) ratifies and confirms its obligations
under its Guaranty, and (d) acknowledges and agrees that it has no claims or
offsets against, or defenses or counterclaims to, its Guaranty.

         9.       EXECUTION IN COUNTERPARTS. This Fourth Amendment may be
executed in any number of counterparts and by different parties hereto in
separate counterparts, each of which when so executed and delivered shall be
deemed to be an original and all of which when taken together shall constitute
but one and the same instrument. For purposes of this Fourth Amendment, a
counterpart hereof (or signature page thereto) signed and transmitted by any
Person party hereto to the Administrative Agent (or its counsel) by facsimile
machine, telecopier or electronic mail is to be treated as an original. The
signature of such Person thereon, for purposes hereof, is to be considered as an
original signature, and the counterpart (or signature page thereto) so
transmitted is to be considered to have the same binding effect as an original
signature on an original document.

         10.      GOVERNING LAW; BINDING EFFECT. This Fourth Amendment shall be
governed by and construed in accordance with the laws of the State of Texas
applicable to agreements made and to be performed entirely within such state,
provided that each party shall

                                       6
<PAGE>

retain all rights arising under federal law, and shall be binding upon the
parties hereto and their respective successors and assigns.

         11.      HEADINGS. Section headings in this Fourth Amendment are
included herein for convenience of reference only and shall not constitute a
part of this Fourth Amendment for any other purpose.

         12.      ENTIRE AGREEMENT. THE CREDIT AGREEMENT, AS AMENDED BY THIS
FOURTH AMENDMENT, AND THE OTHER LOAN DOCUMENTS REPRESENT THE FINAL AGREEMENT
BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS BETWEEN THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

================================================================================
                   REMAINDER OF PAGE LEFT INTENTIONALLY BLANK
================================================================================

                                       7
<PAGE>

         IN WITNESS WHEREOF, this Fourth Amendment is executed as of the date
first set forth above.

                                     ELKCORP

                                     By: _______________________________________
                                          Harold Beattie, Jr.
                                          Senior Vice President, Chief Financial
                                          Officer and Treasurer

                                       8
<PAGE>

                                     BANK OF AMERICA, N.A., as Administrative
                                     Agent

                                     By: _______________________________________
                                          Name:  _______________________________
                                          Title: _______________________________

                                     BANK OF AMERICA, N.A., as a Lender, L/C
                                     Issuer and Swing Line Lender

                                     By: _______________________________________
                                          Name:  _______________________________
                                          Title: _______________________________

                                     BANK ONE, N.A., as a Lender and
                                     Documentation Agent

                                     By: _______________________________________
                                          Name:  _______________________________
                                          Title: _______________________________

                                     THE NORTHERN TRUST COMPANY, as a Lender

                                     By: _______________________________________
                                          Name:  _______________________________
                                          Title: _______________________________

                                       9
<PAGE>

                                     COMERICA BANK-TEXAS, as a Lender

                                     By: _______________________________________
                                          Name:  _______________________________
                                          Title: _______________________________

                                     COMPASS BANK, as a Lender

                                     By: _______________________________________
                                          Name:  _______________________________
                                          Title: _______________________________

                                     HIBERNIA NATIONAL BANK, as a Lender

                                     By: _______________________________________
                                          Name:  _______________________________
                                          Title: _______________________________

                                     WASHINGTON MUTUAL BANK, FA, as a Lender

                                     By: _______________________________________
                                          Name:  _______________________________
                                          Title: _______________________________

                                       10
<PAGE>

                                     BRANCH BANKING AND TRUST COMPANY, as a
                                     Lender

                                     By: _______________________________________
                                          Name:  _______________________________
                                          Title: _______________________________

                                       11
<PAGE>

ACKNOWLEDGED AND AGREED FOR
PURPOSES OF SECTION 5 HEREOF:

WACHOVIA BANK, N.A.

By: _______________________________________
     Name:  _______________________________
     Title: _______________________________

THE FROST NATIONAL BANK

By: _______________________________________
     Name:  _______________________________
     Title: _______________________________

                                       12
<PAGE>

ACKNOWLEDGED AND AGREED TO:

ELK PREMIUM BUILDING PRODUCTS, INC.
         (formerly known as Elk Corporation of Dallas)
ELK CORPORATION OF TEXAS
ELK CORPORATION OF AMERICA
ELK CORPORATION OF ARKANSAS
ELK CORPORATION OF ALABAMA
OEL, LTD.
CHROMIUM CORPORATION
CYBERSHIELD OF GEORGIA, INC.
CYBERSHIELD, INC.
CYBERSHIELD INTERNATIONAL, INC.
CYBERSHIELD OF TEXAS, INC.
(formerly known as Chromium Corporation)
ELK TECHNOLOGY GROUP, INC.
ELK TECHNOLOGIES, INC.
ELK PERFORMANCE NONWOVEN FABRICS, INC.
ELK COMPOSITE BUILDING PRODUCTS, INC.

By: _______________________________________
     Harold Beattie, Jr.
     Vice President for All

NELPA, INC.

By: _______________________________________
     Name:  _______________________________
     Title: _______________________________

                                       13
<PAGE>

ELK GROUP, L.P.
(formerly known as Elcor Service Limited Partnership)

By: ELK GROUP, INC.
    (formerly known as Elcor Management Corporation),
    Its General Partner

By: _______________________________________
    Harold Beattie, Jr.
    Senior Vice President

ELK GROUP, INC.
(formerly known as Elcor Management Corporation)

By: _______________________________________
    Harold Beattie, Jr.
    Senior Vice President

                                       14
<PAGE>

                                                                   SCHEDULE 2.01

                                   COMMITMENTS
                               AND PRO RATA SHARES

<TABLE>
<CAPTION>
         LENDER                           COMMITMENT            PRO RATA SHARE
         ------                           ----------            --------------
<S>                                    <C>                      <C>
Bank of America, N.A.                  $    23,500,000                  23.50%

Bank One, N.A.                         $    18,500,000                  18.50%

Comerica Bank - Texas                  $    14,000,000                  14.00%

The Northern Trust Company             $    11,000,000                  11.00%

Branch Banking and Trust Company       $    10,000,000                  10.00%

Washington Mutual Bank, FA             $    10,000,000                  10.00%

Hibernia National Bank                 $     7,500,000                   7.50%

Compass Bank                           $     5,500,000                   5.50%

                TOTAL                  $100,000,000.00          100.000000000%
</TABLE>

                                  Schedule 2.01

<PAGE>

                                                                       EXHIBIT E

                         FORM OF COMPLIANCE CERTIFICATE

                                         Financial Statement Date: _____________

To:      Bank of America, N.A., as Administrative Agent

Ladies and Gentlemen:

         Reference is made to that certain Credit Agreement, dated as of
____________, 2000 (as amended, restated, extended, supplemented or otherwise
modified in writing from time to time, the "Agreement;" the terms defined
therein being used herein as therein defined), among ElkCorp (the "Borrower"),
the Lenders from time to time party thereto, and Bank of America, N.A., as
Administrative Agent, L/C Issuer and Swing Line Lender.

         The undersigned Responsible Officer hereby certifies as of the date
hereof that he/she is the ___________________of the Borrower, and that, as such,
he/she is authorized to execute and deliver this Certificate to the
Administrative Agent on the behalf of the Borrower, and that:

[Use following for fiscal year-end financial statements]

         1.       Attached hereto as Schedule 1 are the year-end audited
financial statements required by Section 6.01(a) of the Agreement for the fiscal
year of the Borrower ended as of the above date, together with the report and
opinion of an independent certified public accountant required by such section.

[Use following for fiscal QUARTER-END financial statements]

         1.       Attached hereto as Schedule 1 are the unaudited financial
statements required by Section 6.01(b) of the Agreement for the fiscal quarter
of the Borrower ended as of the above date. Such financial statements fairly
present the financial condition, results of operations and cash flows of the
Borrower and its Subsidiaries in accordance with GAAP as at such date and for
such period, subject only to normal year-end audit adjustments and the absence
of footnotes.

         2.       The undersigned has reviewed and is familiar with the terms of
the Agreement and has made, or has caused to be made under his/her supervision,
a detailed review of the transactions and condition (financial or otherwise) of
the Borrower during the accounting period covered by the attached financial
statements.

         3.       A review of the activities of the Borrower during such fiscal
period has been made under the supervision of the undersigned with a view to
determining whether during such fiscal period the Borrower performed and
observed all its Obligations under the Loan Documents, and

[SELECT ONE:]

                                 Exhibit E - 1
<PAGE>

         [TO THE BEST KNOWLEDGE OF THE UNDERSIGNED DURING SUCH FISCAL PERIOD,
THE BORROWER PERFORMED AND OBSERVED EACH COVENANT AND CONDITION OF THE LOAN
DOCUMENTS APPLICABLE TO IT.]

--OR--

         [THE FOLLOWING COVENANTS OR CONDITIONS HAVE NOT BEEN PERFORMED OR
OBSERVED AND THE FOLLOWING IS A LIST OF EACH SUCH DEFAULT OR EVENT OF DEFAULT
AND ITS NATURE AND STATUS:]

         4.       The financial covenant analyses and information set forth on
Schedule 2 attached hereto are true and accurate on and as of the date of this
Certificate.

         IN WITNESS WHEREOF, the undersigned has executed this Certificate as of
____ . ______________, ____________.

                                     ELKCORP

                                     By: _______________________________________
                                          Name:  _______________________________
                                          Title: _______________________________

                                 Exhibit E - 2
<PAGE>

        For the Quarter/Year ended ___________________("Statement Date")

                                   SCHEDULE 2
                          to the Compliance Certificate
                                  ($ in 000's)

<TABLE>
<S>                                                                                             <C>
I.    LEVERAGE RATIO - FOR DETERMINATION OF APPLICABLE RATE

      A.      Consolidated EBITDA for four consecutive fiscal quarters ending on
              above date ("Subject Period"):

              1.       Consolidated Adjusted Net Income for Subject Period:                     $_____________

              2.       Consolidated Interest Expense for Subject Period:                        $_____________

              3.       Provision for income taxes for Subject Period:                           $_____________

              4.       Depreciation expenses and Amortization expenses for intangibles          $_____________
                       for Subject Period:

              5.       Trailing 4 fiscal quarters of Consolidated EBITDA of assets              $_____________
                       acquired during Subject Period:

              6.       Trailing 4 fiscal quarters of Consolidated EBITDA of assets              $_____________
                       disposed of during Subject Period:

              7.       Consolidated EBITDA (lines I.A 1 + 2 + 3 + 4 + 5 + 6):                   $_____________

      B.      Consolidated Funded Indebtedness at Statement Date:                               $_____________

      C.      Leverage Ratio (Line I.A.7 / Line I.B.):                                          $_____________

II.   SECTION 7.05 - RESTRICTED PAYMENTS.

      A.      Base:                                                                             $15,000,000

      B.      35% of cumulative Consolidated Net Income (100% in case of a deficit)             $_____________
              commencing July 1, 2000:

      C.      Amounts received from sale or disposition of Capital Stock acquired in a          $_____________
              Treasury Stock Purchase:

      D.      Amount Available for Restricted Payments (Lines II.A. + (or minus if a            $_____________
              deficit) II.B. + II.C.):
</TABLE>

                                 Exhibit E - 3
<PAGE>

<TABLE>
<S>                                                                                             <C>
      E.      Restricted Payments made during term of Agreement:                                $_____________

      F.      Excess Available for Restricted Payments (Line II.D. - II.E.):                    $_____________

III.  SECTION 7.12(a) - CONSOLIDATED NET WORTH.

      A.      Actual Consolidated Net Worth at Statement Date:                                  $_____________

      B.      50% of Consolidated Net Income for each fiscal year ending after June             $_____________
              30, 2001 (no reduction for losses):

      C.      100% of increases in Shareholders' Equity after date of Agreement from            $_____________
              issuance and sale of capital stock (including from conversion of debt
              securities, but excluding treasury stock):

      D.      Minimum required Consolidated Net Worth (Lines III.B + III.C plus                 $_____________
              $130,000,000):

      E.      Excess (deficient) for covenant compliance (Line III.A - III.D):                  $_____________

IV.   SECTION 7.13(b) - FIXED CHARGE COVERAGE RATIO.

      A.      Consolidated EBITDA for four consecutive fiscal quarters ending on above          $_____________
              date ("Subject Period") (Line I.A.7 above):

      B.      Cash Taxes of Borrower and its Subsidiaries for Subject Period:                   $_____________

      C.      Maintenance Capital Expenditures for Subject Period:                              $12,000,000

      D.      Consolidated Interest Charges for Subject Period:                                 $_____________

      E.      Principal payments of Indebtedness of the Borrower and its Subsidiaries           $_____________
              required to be paid during Subject Period:

      F.      Fixed Charge Coverage Ratio (Lines IV. A. - IV.B. - IV.C.) / (Lines               ______ to 1
              (IV.D. + IV.E.):

      G.      Fixed Charge Coverage Ratio for immediately preceding two consecutive             ______ to 1
              fiscal quarters
                                                                                                ______ to 1
</TABLE>

                                 Exhibit E - 4

<PAGE>

Minimum required:

<TABLE>
                                                      MINIMUM FIXED
                                                     CHARGE COVERAGE
                                                          RATIO
-----------------------------------------------------------------------
<S>                                                <C>
Each fiscal quarter                                     1.50 to 1

For each fiscal quarter after Fixed Charge              1.75 to 1
Coverage Ratio for the immediately preceding
two consecutive fiscal quarters was less than
1.75 to 1
</TABLE>

<TABLE>
<S>                                                                                             <C>
V.    SECTION 7.13(c) - CAPITALIZATION RATIO.

      A.      Consolidated Funded Indebtedness at Statement Date:                               $_____________

      B.      Capitalization:

              1.       Consolidated Funded Indebtedness at Statement Date:                      $_____________

              2.       Consolidated Net Worth (Line III.A. above)                               $_____________

              3.       Capitalization (Lines V.B. 1 + 2):                                       $_____________

      C.      Capitalization Ratio (Line V.A) / (Line V.B.3):                                   _____ to 1
</TABLE>

Maximum allowed:
<TABLE>
                                                         MAXIMUM
                                                     CAPITALIZATION
-----------------------------------------------------------------------
<S>                                              <C>
Any fiscal quarter                                      0.55 to 1
</TABLE>

                                 Exhibit E - 5<PAGE>
                                                                    EXHIBIT 10.1

                                                                  EXECUTION COPY

                                 FIRST AMENDMENT

         This FIRST AMENDMENT (this "Amendment") is entered into effective as of
December 23, 2002, in respect of the Uncommitted Amended and Restated Credit
Agreement, dated as of July 1, 2002 (as amended, supplemented or otherwise
modified prior to the date hereof, the "Credit Agreement") among WOODWARD
MARKETING, L.L.C., a Delaware limited liability company (the "Borrower"), the
financial institutions parties thereto (the "Banks"), FORTIS CAPITAL CORP., a
Connecticut corporation ("Fortis"), as a Bank, as an Issuing Bank, as Collateral
Agent and as Administrative Agent for the Banks, and BNP PARIBAS, a bank
organized under the laws of France ("BNP Paribas"), as a Bank, as an Issuing
Bank, and as Documentation Agent.

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

         NOW, THEREFORE, in consideration of premises and for other good and
valuable consideration, the receipt and sufficiency of which is hereby
acknowledged, the Borrower, Fortis, BNP Paribas and the other Banks agree as
follows:

         1. Defined Terms. Unless otherwise defined herein, terms defined in the
Credit Agreement are used herein as therein defined.

         2. Amendments. The Credit Agreement is hereby amended as follows:

                  (a) The definition of "Expiration Date" in Section 1.01,
Certain Defined Terms, is hereby amended by deleting the date "December 31,
2002" in subsection (a) and substituting in lieu thereof "February 28, 2003".

                  (b) The definition of "Maturity Date" in Section 1.01, Certain
Defined Terms, is hereby amended by deleting the date "March 31, 2003" and
substituting in lieu thereof "May 31, 2003".

         3. Representations. To induce the Administrative 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 Administrative Agent and 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.

                                       1
<PAGE>

         4. Conditions Precedent. As a condition to Administrative Agent and the
Banks entering into this Amendment, the Administrative Agent and the Banks must
have received executed originals of each of the following documents and
instruments, in form and substance satisfactory to the Administrative Agent and
the Banks:

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

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

         5. Miscellaneous.

                  (a) No Other Amendments or Waivers. Except as expressly
consented to hereby, the Credit Agreement and the other Loan Documents shall
remain in full force and effect in accordance with their respective terms,
without any consent, amendment, waiver or modification of any provision thereof.

                  (b) 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.

                  (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. Delivery of an executed counterpart of a
signature page to this Amendment by telecopier shall be effective as delivery of
an originally executed counterpart of this Amendment.

                  (d) Governing Law. This Amendment shall be construed in
accordance with and governed by the laws of the State of New York (without
reference to principles of conflicts of laws); provided, however, that the
Administrative Agent, the 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, Administrative Agent, the
Banks, 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.

                            [SIGNATURE PAGES FOLLOW]

                                       2
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed and delivered by their proper and duly authorized officers as of
the day and year first above written.

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

                                       By:    /s/ RONALD  W. BAHR
                                              ----------------------------------
                                       Name:  Ronald W. Bahr
                                              ----------------------------------
                                       Title: Senior Vice President
                                              ----------------------------------

                                       Borrower's Address:
                                       11251 Northwest Freeway, Suite 400
                                       Houston, Texas 77092
                                       Attention: Ronald W. Bahr
                                       Telephone: (713) 688-7771
                                       Facsimile: (713) 688-5124

                                       FORTIS CAPITAL CORP.,
                                       a Connecticut corporation
                                       as Administrative Agent, Collateral
                                       Agent, Issuing Bank and a Bank

                                       By: /s/ IRENE C. RUMMEL
                                           -------------------------------------
                                           Name:  Irene C. Rummel
                                           Title: Senior Vice President

                                       By: /s/ LEONARD RUSSO
                                           -------------------------------------
                                           Name:  Leonard Russo
                                           Title: Director

                                       100 Crescent Court
                                       Suite 1777
                                       Dallas, TX 75201
                                       Telephone: (214) 953-9314
                                       Facsimile: (214) 969-9332

                    [Signatures continue on following page.]

                         [Amendment to Credit Agreement]

                                       3
<PAGE>

                                       BNP PARIBAS,
                                       a bank organized under the laws of France
                                       as a Bank, Issuing Bank, and
                                       Documentation Agent

                                       By:    /s/ ZALI WIN
                                              ----------------------------------
                                       Name:  Zali Win
                                              ----------------------------------
                                       Title: Director
                                              ----------------------------------

                                       787 Seventh Avenue
                                       New York, New York 10019
                                       Attention: Zali Win
                                       Telephone: (212) 841-2020
                                       Facsimile: (212) 841-2536

                                       BNP PARIBAS,
                                       a bank organized under the laws of France
                                       as a Bank, Issuing Bank, and
                                       Documentation Agent

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

                                       787 Seventh Avenue
                                       New York, New York 10019
                                       Attention: Ed Chin
                                       Telephone: (212) 841-2020
                                       Facsimile: (212) 841-2536

                    [Signatures continue on following page.]

                         [Amendment to Credit Agreement]

                                       4
<PAGE>

                                       SOCIETE GENERALE,
                                       as a Bank

                                       By:    /s/ BARBARA PAULSEN
                                              ----------------------------------
                                       Name:  Barbara Paulsen
                                              ----------------------------------
                                       Title: VP
                                              ----------------------------------

                                       1221 Avenue of the Americas
                                       New York, New York 10020
                                       Attention: Barbara Paulsen
                                       Telephone: (212) 278-6496
                                       Facsimile: (212) 278-7417

                                       SOCIETE GENERALE,
                                       as a Bank

                                       By:    /s/ EMMANUEL CHESNEAU
                                              ----------------------------------
                                       Name:  Emmanuel Chesneau
                                              ----------------------------------
                                       Title: Director
                                              ----------------------------------

                                       1221 Avenue of the Americas
                                       New York, New York 10020
                                       Attention: Emmanuel Chesneau
                                       Telephone: (212) 278-6496
                                       Facsimile: (212) 278-7417

                    [Signatures continue on following page.]

                         [Amendment to Credit Agreement]

                                       5
<PAGE>

                                       NATEXIS BANQUES POPULAIRES, NEW YORK
                                       BRANCH, as a Bank

                                       By:    /s/ DAVID PERSHAD
                                              ----------------------------------
                                       Name:  David Pershad
                                              ----------------------------------
                                       Title: Vice President
                                              ----------------------------------

                                       1251 Avenue of the Americas, 34th Floor
                                       New York, New York 10020
                                       Attention: David Pershad
                                       Telephone: (212) 872-5015
                                       Facsimile: (212) 354-9095

                                       NATEXIS BANQUES POPULAIRES, NEW YORK
                                       BRANCH, as a Bank

                                       By:    /s/ GUILLAUME DE PARSCAU
                                              ----------------------------------
                                       Name:  Guillaume de Parscau
                                              ----------------------------------
                                       Title: First Vice President & Manager
                                              ----------------------------------
                                              Commodities Finance Group
                                              ----------------------------------

                                       1251 Avenue of the Americas, 34th Floor
                                       New York, New York 10020
                                       Attention: Guillaume de Parscau
                                       Telephone: (212) 872-5015
                                       Facsimile: (212) 354-9095

                    [Signatures continue on following page.]

                         [Amendment to Credit Agreement]

                                       6
<PAGE>

                                       RZB FINANCE LLC,
                                       as a Bank

                                       By:    /s/ HERMINE KIROLOS
                                              ----------------------------------
                                       Name:  Hermine Kirolos
                                              ----------------------------------
                                       Title: Group Vice President
                                              ----------------------------------

                                       1133 Avenue of the Americas
                                       New York, New York 10036
                                       Attention: Hermine Kirolos
                                       Telephone: (212) 845-4114
                                       Facsimile: (212) 944-6389

                                       RZB FINANCE LLC,
                                       as a Bank

                                       By:    /s/ PEARL GETTERS
                                              ----------------------------------
                                       Name:  Pearl Getters
                                              ----------------------------------
                                       Title: First Vice President
                                              ----------------------------------

                                       1133 Avenue of the Americas
                                       New York, New York 10036
                                       Attention: Pearl Getters
                                       Telephone: (212) 845-4114
                                       Facsimile: (212) 944-6389

                    [Signatures continue on following page.]

                         [Amendment to Credit Agreement]

                                       7
<PAGE>

                                       GUARANTORS:

                                       ATMOS ENERGY MARKETING, LLC

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

                                       1800 Three Lincoln Centre
                                       5430 LBJ Freeway
                                       Dallas, TX 75240

                                       ATMOS ENERGY HOLDINGS, INC.

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

                                       1800 Three Lincoln Centre
                                       5430 LBJ Freeway
                                       Dallas, TX 75240

                         [Amendment to Credit Agreement]

                                       8

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