Document:

<PAGE>
                                                                   Exhibit 10.31

                       THIRD AMENDMENT TO CREDIT AGREEMENT

         THIS THIRD AMENDMENT TO CREDIT AGREEMENT (herein called this
"Amendment") is made as of December 12, 2002 by and between North Coast Energy,
Inc., a Delaware corporation ("Borrower"), and Union Bank of California, N.A.,
as Agent (herein called "Agent"), and the other Lenders from time to time
parties to the Credit Agreement (as defined below).

                              W I T N E S S E T H:

         WHEREAS, Borrower, Agent and Lenders have entered into that certain
Credit Agreement dated as of September 26, 2000 (as amended, supplemented, or
restated to the date hereof, the "Original Agreement"), for the purposes and
consideration therein expressed, pursuant to which Lenders became obligated to
make loans to Borrower as therein provided; and

         WHEREAS, Borrower, Agent, and Lenders desire to amend the Original
Agreement as provided herein.

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants and agreements contained herein and in the Original Agreement, in
consideration of the loans which may hereafter be made by Lenders to Borrower,
and for other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, the parties hereto do hereby agree as follows:

                                   ARTICLE I.

                           DEFINITIONS AND REFERENCES

         ss. 1.1 TERMS DEFINED IN THE ORIGINAL AGREEMENT. Unless the context
otherwise requires or unless otherwise expressly defined herein, the terms
defined in the Original Agreement shall have the same meanings whenever used in
this Amendment.

         ss. 1.2. OTHER DEFINED TERMS. Unless the context otherwise requires,
the following terms when used in this Amendment shall have the meanings assigned
to them in this ss.1.2.

                  "AMENDMENT" means this Third Amendment to Credit Agreement.

                  "CREDIT AGREEMENT" means the Original Agreement as amended
hereby.

<PAGE>

                                   ARTICLE II.

                        AMENDMENTS TO ORIGINAL AGREEMENT

         ss. 2.1. DEFINED TERM. The definition of the term "CONSOLIDATED EBITDA"
in Section 1.1 of the Original Agreement is hereby deleted and replaced with the
following definition of the term "CONSOLIDATED EBITDAX":

         "CONSOLIDATED EBITDAX" means, for each period of four consecutive
         Fiscal Quarters, the sum of (1) the Consolidated Net Income of Borrower
         during such period, plus (2) all interest expense which was deducted in
         determining such Consolidated Net Income, plus (3) all income taxes
         which were deducted in determining such Consolidated Net Income, plus
         (4) all depreciation, amortization (including amortization of good will
         and debt issue costs) and other non-cash charges (including any
         provision for the reduction in the carrying value of assets recorded in
         accordance with GAAP) which were deducted in determining such
         Consolidated Net Income, plus (5) all exploration and abandonment
         expense which were deducted in determining such Consolidated Net
         Income, minus (6) all non-cash items of income which were included in
         determining such Consolidated Net Income.

         ss. 2.2. INTEREST COVERAGE RATIO. Section 7.14 of the Original
Agreement is hereby amended in its entirety to read as follows:

         Section 7.14. INTEREST COVERAGE RATIO. At the end of any Fiscal
         Quarter, the ratio of (a) Borrower's Consolidated EBITDAX for the four
         immediately preceding consecutive fiscal quarters to (b) Borrower's
         Consolidated Interest Expense for such period will never be less than
         2.5 to 1.0

         ss. 2.3. FIXED CHARGE COVERAGE RATIO. Section 7.15 of the Original
Agreement is hereby amended in its entirety to read as follows:

         Section 7.15. FIXED CHARGE COVERAGE RATIO. At the end of any Fiscal
         Quarter, the ratio of (a) Borrower's Consolidated EBITDAX for the four
         immediately preceding consecutive Fiscal Quarters to (b) Borrower's
         Consolidated Fixed Charges for such period will never be less than 1.5
         to 1. For purposes of this section, "Borrower's Consolidated Fixed
         Charges" means the sum of Borrower's Consolidated Interest Expense,
         payments of principal on Indebtedness (other than under this agreement
         if the Borrower has the right to redraw the amount so paid), income
         taxes paid in cash and dividends on Preferred Stock accrued during such
         period, but only to the extent paid in cash during the next Fiscal
         Quarter.

         ss. 2.4. LIMITATION ON SALES OF PROPERTY. Section 7.5 of the Original
Agreement is hereby amended to add the following paragraph (f) immediately
following paragraph (e):

                           (f) other property (including Collateral, which
                  shall be released from the

                                      -2-
<PAGE>

                  Liens of the Security Documents) which is sold for fair
                  consideration not in excess of $500,000 in the aggregate
                  (taking into account all such sales of all Restricted Persons)
                  during the six month period between any two Determination
                  Dates.

                                  ARTICLE III.

                           CONDITIONS OF EFFECTIVENESS

         ss. 3.1. CONDITIONS OF EFFECTIVENESS. This Amendment shall become
effective as of the date first above written when and only when each of the
following conditions shall have been satisfied:

                  (a) Agent shall have received, at Agent's office, each of the
         following in form, substance and date satisfactory to Agent: (i) a
         counterpart of this Amendment executed and delivered by Borrower and
         Majority Lenders; and (ii) a certificate of a duly authorized officer
         of Borrower dated the date of this Amendment certifying: (A) that all
         of the representations and warranties set forth in ss. 4.1 hereof are
         true and correct at and as of the time of such effectiveness; and (B)
         as to such other corporate matters as Agent shall deem necessary; and

                  (b) Agent shall have additionally received such other
         documents as Agent may reasonably request.

                                   ARTICLE IV.

                         REPRESENTATIONS AND WARRANTIES

         ss. 4.1. REPRESENTATIONS AND WARRANTIES OF BORROWER. In order to induce
Agent and Lenders to enter into this Amendment, Borrower represents and warrants
as of the date on which this Amendment becomes effective to Agent that:

                  (a) The representations and warranties contained in Article V
         of the of the Credit Agreement are true and correct at and as of the
         time of the effectiveness hereof.

                  (b) Each Restricted Person is duly authorized to execute and
         deliver each Loan Document to which it is a party and Borrower is and
         will continue to be duly authorized to borrow and to perform its
         obligations under the Credit Agreement. Each Restricted Person has duly
         taken all corporate action necessary to authorize the execution and
         delivery of each Loan Document to which it is a party and to authorize
         the performance of the obligations of it hereunder and thereunder.

                  (c) The execution and delivery by each Restricted Person of
         the Loan Documents to which it is a party, the performance by each
         Restricted Person of its obligations hereunder

                                      -3-
<PAGE>

         and thereunder, and the consummation of the transactions contemplated
         hereby and thereby do not and will not conflict with any provision of
         law, statute, rule or regulation or of the articles of incorporation
         and bylaws of any Restricted Person, or of any material agreement,
         judgment, license, order or permit applicable to or binding upon any
         Restricted Person, or result in the creation of any lien, charge or
         encumbrance upon any assets or properties of any Restricted Person.
         Except for those which have been duly obtained, no consent, approval,
         authorization or order of any court or governmental authority or third
         party is required in connection with the execution and delivery by any
         Restricted Person of the Loan Documents to which it is a party, or to
         consummate the transactions contemplated hereby and thereby.

                  (d) When duly executed and delivered, each of this Amendment
         and each Loan Document (as amended or affected by this by the
         Amendment) will be a legal and binding instrument and agreement of each
         Restricted Person that is a party thereto, enforceable in accordance
         with its terms, except as limited by bankruptcy, insolvency and similar
         laws applying to creditors' rights generally and by principles of
         equity applying to creditors' rights generally.

                  (e) The audited annual financial statements of Borrower dated
         as of March 31, 2002 and the unaudited quarterly financial statements
         of Borrower dated as September 30, 2002 fairly present the financial
         position at such dates and the statement of operations and the changes
         in financial position for the periods ending on such dates for
         Borrower. Copies of such financial statements have heretofore been
         delivered to Agent. Since March 31, 2002, no material adverse change
         has occurred in the financial condition or businesses of Borrower.

                                   ARTICLE V.

                                  MISCELLANEOUS

         ss. 5.1. RATIFICATION OF AGREEMENTS. Each Loan Document, as amended or
affected hereby, is hereby ratified and confirmed in all respects. Any reference
to the Credit Agreement in any Loan Document shall be deemed to refer to this
Amendment also. The execution, delivery and effectiveness of this Amendment
shall not, except as expressly provided herein or therein, operate as a waiver
of any right, power or remedy of Agent or Lenders under the Credit Agreement or
any other Loan Document nor constitute a waiver of any provision of the Credit
Agreement or any other Loan Document.

         ss. 5.2. SURVIVAL OF AGREEMENTS. All representations, warranties,
covenants and agreements of Borrower herein shall survive the execution and
delivery of this Amendment and the performance hereof, including without
limitation the making or granting of the Loan, and shall further survive until
all of the Obligations are paid in full. All statements and agreements contained
in any certificate or instrument delivered by any Restricted Person hereunder or
under the Credit Agreement to Agent shall be deemed to constitute
representations and warranties by, or agreements and covenants of, Borrower
under this Amendment and under the Credit Agreement.

                                      -4-
<PAGE>

         ss. 5.3. LOAN DOCUMENTS. This Amendment is a Loan Document, and all
provisions in the Credit Agreement pertaining to Loan Documents apply hereto and
thereto.

         ss. 5.4 GOVERNING LAW. This Amendment shall be governed by and
construed in accordance with the laws of the State of Texas and any applicable
laws of the United States of America in all respects, including construction,
validity and performance.

         ss. 5.5. COUNTERPARTS. This Amendment may be separately executed in
counterparts and by the different parties hereto in separate counterparts, each
of which when so executed shall be deemed to constitute one and the same
Amendment.

         THIS 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 OF THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS OF THE PARTIES.

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

                                   NORTH COAST ENERGY, INC.

                                   By: /s/ Omer Yonel
                                   -----------------------------------
                                   Name: Omer Yonel
                                   Title: Chief Executive Officer, Director

                                   UNION BANK OF CALIFORNIA, N.A., as
                                   Agent and Lender

                                   By: /s/ Randall Osterberg
                                   -----------------------------------
                                   Name: Randall Osterberg
                                   Title: Senior Vice President

                                   By: /s/ John A. Clark
                                   -----------------------------------
                                   Name: John A. Clark
                                   Title: Vice President

                                      -5-
<PAGE>

                                        BANK ONE, NA (Main Office Chicago),
                                        Lender

                                        By: /s/ Thomas E. Okamoto
                                           ----------------------------------
                                           Name: Thomas E. Okamoto
                                           Title: Associate Director

                                        COMERICA BANK-TEXAS, Lender

                                        By: /s/ Huma Vadgama
                                           ----------------------------------
                                           Name: Huma Vadgama
                                           Title: Assistant Vice President

                                        FORTIS CAPITAL CORP., Lender

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

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

                                      -6-
<PAGE>

                             CONSENT AND AGREEMENT

         North Coast Operating Company (the "Company") and each of the
partnerships party hereto (the "Partnerships") hereby consent to the provisions
of this Amendment and the transactions contemplated herein, and agrees that the
Company's and the Partnership's obligations and covenants under the Credit
Agreement are unimpaired hereby and shall remain in full force and effect. North
Coast Energy Eastern, Inc., f/k/a Peake Energy, Inc., hereby consents to the
provisions of this Amendment and the transactions contemplated herein, and
agrees that its obligations and covenants under its Guaranty of even date with
the Original Agreement in favor of Agent are unimpaired hereby and shall remain
in full force and effect.

Date: December 12, 2002

NORTH COAST ENERGY EASTERN, INC.         NORTH COAST OPERATING COMPANY

By: /s/ Omer Yonel                          By: /s/ Omer Yonel
   ---------------------------              ----------------------------
   Name:                                    Name:
   Title:                                   Title:

Capital Drilling Fund 1986-1
Limited Partnership

North Coast Energy 1996-1 Appalachian
Private Drilling Program L.P.

North Coast Energy 1996-2 Appalachian
Private Drilling Program L.P.

North Coast Energy 1997-2 Appalachian
Private Drilling Program L.P.

By: NORTH COAST ENERGY, INC., general partner

   By: /s/ Omer Yonel
      --------------------------
      Name:
      Title:

                                       1<PAGE>
                                                                     EXHIBIT 4.5

                                 AMENDMENT NO. 1
                                       TO
                                 NOTE AGREEMENT

      This AMENDMENT NO. 1 TO NOTE AGREEMENT (this "Amendment"), dated as of
September 25, 1996, is made by and among GENENCOR INTERNATIONAL, INC., a
Delaware corporation (together with its successors and assigns, the "Company"),
and each of the institutions that are signatories hereto (such institutions
being collectively referred to as the "Noteholders").

                                   BACKGROUND

      1. The Company and each of the Noteholders are parties to the Note
Agreement (the "Existing Note Agreement"), dated as of March 28, 1996, that
provides, among other things, for the sale by the Company and the purchase by
the Noteholders of One Hundred Forty Million Dollars ($140,000,000) in aggregate
principal amount of the Company's 6.82% Senior Notes due March 30, 2006 (the
"Notes").

      2. The Company has requested that the Existing Note Agreement be amended
as provided in this Amendment.

      NOW, THEREFORE, in order to induce the Noteholders to amend the Existing
Note Agreement and in consideration of other good and valuable consideration
(the receipt and sufficiency of which are hereby acknowledged), the Company
agrees with the Noteholders as follows:

SECTION 1. DEFINED TERMS.

      All capitalized terms used, but not specifically defined, in this
Amendment have the respective meanings assigned to them in or pursuant to the
provisions of the Existing Note Agreement as amended by this Amendment (the
Existing Note Agreement, as so amended, being referred to as the "Amended Note
Agreement").

SECTION 2. AMENDMENT TO EXISTING NOTE AGREEMENT.

      Paragraph 6B of the Existing Note Agreement is hereby amended and restated
in its entirety to read as follows:

            "6B. EBITDA LEVERAGE MAINTENANCE TEST. The Company will not permit
      the ratio of

            (i) Consolidated Indebtedness, determined as of the end of any
      fiscal quarter of the Company, to

            (ii) EBITDA for the period of four (4) consecutive fiscal quarters
      ending with such fiscal quarter,

to be greater than (a) 4.75 to 1.00, as of the end of any fiscal quarter ending
at any time from and including September 30, 1996 to and including June 30,
1997, (b) 4.50 to 1.00, as of the end of either fiscal quarter ending on and
including September 30, 1997 or December 31, 1997, or (c) 3.50 to 1.00, as of
the end of any fiscal quarter ending on or after March 31, 1998."

<PAGE>

SECTION 3. WARRANTIES AND REPRESENTATIONS.

      The Company warrants and represents to each Noteholder that as of the date
of this Amendment and as of the Effective Date (as defined in Section 4):

      3.1 NO MATERIAL ADVERSE CHANGE. There has been no material adverse change
in the business, condition or operations (financial or otherwise) of the Company
and its Subsidiaries taken as a whole since December 31, 1995.

      3.2 NO DEFAULTS. No event has occurred and no condition exists that, on
the Effective Date, would constitute a Default or Event of Default.

      3.3 AMENDMENT IS ENFORCEABLE. This Amendment and the Amended Note
Agreement are legal, valid and binding and enforceable obligations of the
Company, enforceable against the Company in accordance with their respective
terms, except as the enforceability hereof and of the Amended Note Agreement may
be limited by applicable bankruptcy, reorganization, arrangement, insolvency,
moratorium or other similar laws affecting the enforceability of creditors'
rights generally and the application of general equitable principles.

SECTION 4. EFFECTIVENESS OF AMENDMENT.

      This Amendment shall have no effect until the Company and the Required
Holders shall have executed and delivered this Amendment (such time of
effectiveness is referred to as the "Effective Date").

SECTION 5. EFFECT OF AMENDMENT.

      Except as expressly provided in this Amendment, the Existing Note
Agreement and the Notes shall remain in full force and effect, without
modification or amendment. This Amendment shall be binding upon, and shall inure
to the benefit of, the successors and assigns of the parties hereto and the
holders from time to time of the Notes.

SECTION 6. EXPENSES.

      The Company shall promptly (and in any event within thirty (30) days of
receiving any statement or invoice therefor) pay all out-of-pocket expenses
relating to this Amendment, including but not limited to the fees and
disbursements of Hebb & Gitlin, special counsel to the Noteholders. The
obligations of the Company under this Section 6 shall survive the termination of
this Amendment.

SECTION 7. SURVIVAL.

      All warranties. representations. certifications and covenants made by the
Company in this Amendment or in any certificate or other instrument delivered by
the Company or on its behalf under this Amendment shall be considered to have
been relied upon by the Noteholders and shall survive the execution of this
Amendment, regardless of any investigation made by or on behalf of any
Noteholder. All statements in any such certificate or other instrument shall
constitute warranties and representations of the Company under this Amendment.

<PAGE>

SECTION 8. DUPLICATE ORIGINALS; EXECUTION IN COUNTERPART.

      Two or more duplicate originals of this Amendment may be signed by the
parties, each of which shall be an original but all of which together shall
constitute one and the same instrument.

      This Amendment may be executed in one or more counterparts and shall be
effective when at least one counterpart shall have been executed by each party
to this Amendment, and each set of counterparts which, collectively, show
execution by each such party to this Amendment shall constitute one duplicate
original.

SECTION 9. GOVERNING LAW.

      This Amendment shall be construed and enforced in accordance with, and the
rights of the parties shall be governed by, the internal law of the State of New
York.

      [REMAINDER OF PAGE INTENTIONALLY BLANK. NEXT PAGE IS SIGNATURE PAGE.]

<PAGE>

      IN WITNESS WHEREOF, the Company and the Noteholders have executed this
Amendment as of the date first above written.

GENENCOR INTERNATIONAL, INC.

By:      /s/ Robert S. Graff
       --------------------------------

Name:  Robert S. Graff

Title: Senior Vice President and Chief
       Financial Officer

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]

<PAGE>

THE PRUDENTIAL INSURANCE COMPANY OF AMERICA

By:      /s/ Kevin J. Kraska
       --------------------------------

Name:  Kevin J. Kraska

Title: Vice President

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]
<PAGE>

THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY

By:      /s/ J. Thomas Christofferson
       --------------------------------
Name:  J. Thomas Christofferson

Title: Vice President

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]
<PAGE>

ALLMERICA FINANCIAL LIFE INSURANCE AND ANNUITY COMPANY

By:      /s/ John P. Kavanaugh
       --------------------------------

Name:  John P. Kavanaugh

Title: Vice President

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]
<PAGE>

FIRST ALLMERICA FINANCIAL LIFE INSURANCE COMPANY

By:      /s/ Scott C. Hyney
       --------------------------------

Name:  Scott C. Hyney

Title: Assistant Vice President

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]

<PAGE>

THE HANOVER INSURANCE COMPANY

By:      /s/ William K. Fain
       --------------------------------

Name:  William K. Fain

Title: Assistant Treasurer

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]
<PAGE>

CONNECTICUT GENERAL LIFE INSURANCE COMPANY
        BY CIGNA INVESTMENTS, INC.

By:      /s/ Stephen L. Roberts
       --------------------------------

Name:  Stephen L. Roberts

Title: Vice President

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]
<PAGE>

CITIZENS INSURANCE COMPANY OF AMERICA

By:      /s/ William K. Fain
       --------------------------------

Name:  William K. Fain

Title: Assistant Treasurer

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]
<PAGE>

CONNECTICUT GENERAL LIFE INSURANCE COMPANY, ON
       BEHALF OF ONE OR MORE SEPARATE ACCOUNTS
       BY CIGNA INVESTMENTS, INC.

By:      /s/ Stephen L. Roberts
       --------------------------------

Name:  Stephen L. Roberts

Title: Vice President

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]
<PAGE>

LIFE INSURANCE COMPANY OF NORTH AMERICA
       BY CIGNA INVESTMENTS, INC.

By:      /s/ Stephen L. Roberts
       --------------------------------

Name:  Stephen L. Roberts

Title: Vice President

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]

<PAGE>

AMERICAN REPUBLIC INSURANCE COMPANY

By:      /s/ G.F. Sheldon
       --------------------------------

Name:  G.F. Sheldon

Title: Senior Vice President, Investments

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]
<PAGE>

UNITED OF OMAHA LIFE INSURANCE COMPANY

By:      /s/ Curt Caldwell
       --------------------------------

Name:  Curt Caldwell

Title: First Vice President

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]
<PAGE>

COMPANION LIFE INSURANCE COMPANY

By:      /s/ Edwin H. Garrison , Jr.
       --------------------------------

Name:  Edwin H. Garrison , Jr.

Title: First Vice President

COMPANION LIFE INSURANCE COMPANY

By:      /s/ Richard A. Witt
       --------------------------------

Name:  Richard A. Witt

Title: Second Vice President
       & Assistant Treasurer

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]
<PAGE>

PACIFIC MUTUAL LIFE INSURANCE COMPANY

By:      /s/ Diane W. Dales
       --------------------------------

Name:  Diane W. Dales

Title: Assistant Vice President

By:      /s/ Audrey L. Milfs
       --------------------------------

Name:  Audrey L. Milfs

Title: Corporate Secretary

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]

<PAGE>

THE OHIO CASUALTY INSURANCE COMPANY

By:      /s/ Richard B. Kelly
       --------------------------------

Name:  Richard B. Kelly

Title: Senior Investment Officer

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]

<PAGE>

BERKSHIRE LIFE INSURANCE COMPANY

By:      /s/ Ellen I. Whittaker
       --------------------------------

Name:  Ellen I. Whittaker

Title: Investment Officer

       [AMENDMENT NO. 1 TO NOTE AGREEMENT OF GENENCOR INTERNATIONAL, INC.]

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