<PAGE>
                                                                   EXHIBIT 10.1


                           FIRST AMENDMENT AND WAIVER

         THIS FIRST AMENDMENT AND WAIVER (this "Amendment") dated as of August
6, 2004 (the "Amendment Effective Date"), is by and among Willbros Group, Inc.,
a Republic of Panama corporation (herein referred to as the "Company"); the
financial institutions parties hereto which are Banks under the Credit
Agreement (as defined below); and Calyon New York Branch (formerly known as
Credit Lyonnais New York Branch), as administrative agent for the Banks (in
such capacity, the "Agent"), and amends the Amended and Restated Credit
Agreement dated as of March 12, 2004, among the Company, the Designated
Subsidiaries from time to time (WGI and such Designated Subsidiaries
collectively, the "Obligors" and individually, an "Obligor"); the several
financial institutions from time to time parties thereto as Banks, Calyon New
York Branch (formerly known as Credit Lyonnais New York BRANCH), as a Bank, as
Issuing Bank (as defined herein), as Agent, and as Lead Arranger and Book
Runner; and CIBC, Inc., as Syndication Agent

                             PRELIMINARY STATEMENTS

         WHEREAS, the Company has requested a revision to and waiver of certain
covenants under the Credit Agreement and the calculation of the Net Borrowing
Base.

         WHEREAS, the Company has requested the Banks to enter into this
Amendment in connection with the foregoing;

                                   AGREEMENT

         NOW THEREFORE, in consideration of the premises and the mutual
covenants contained herein, and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto,
intending to be legally bound, hereby agree as follows. Capitalized terms used
but not otherwise defined herein shall have the meanings assigned such terms in
the Credit Agreement.

         Section 1. Waiver. The Banks hereby waive (and ratify any prior
waivers for) any Default or Event of Default that may have occurred as a result
of noncompliance by the Company with its covenant in Section 9.11(b)(ii) for
the quarter ending June 30, 2004 prior to amendment of said section and
covenant as provided herein.

         Section 2. Amendment of Credit Agreement. The Credit Agreement is
hereby amended, effective as of the Amendment Effective Date, as follows:

         (a) Section 1.1. The following defined terms are hereby amended and
restated in their entirety as set forth below:

              "Fixed Charge Coverage Ratio" means, for any period, the ratio of
         (i) Adjusted EBITDA less Net Capital Expenditures (as defined below)
         to (ii) fixed charges (where fixed charges include Consolidated
         Interest Expense, scheduled

<PAGE>

         principal repayments and cash dividends paid in the trailing four
         quarters of the Company). For purposes of this definition, "Net
         Capital Expenditures" equals Capital Expenditures in the trailing four
         quarters of the Company minus cash and cash equivalents as reported on
         the most recent quarterly financial statement of the Company in excess
         of $10,000,000 (provided that in no event may Net Capital Expenditures
         be less than zero).

         "Net Borrowing Base" means, for any day of determination thereof:

              (a) if the Company has provided a timely Borrowing Base
         Certificate in accordance with Section 4.2 hereof on or prior to such
         day, an amount equal to the "Net Borrowing Base" set forth in the most
         recently delivered Borrowing Base Certificate, which shall be
         calculated to equal the lesser of (i) the Gross Borrowing Base less
         Local Debt as of the Calculation Date of such Borrowing Base
         Certificate or (ii) an amount equal to a multiple of Adjusted EBITDA
         less Local Debt as of the Calculation Date of such Borrowing Base
         Certificate, where the multiple for Adjusted EBITDA will be as
         follows:

              (A) for the four quarter period ending June 30, 2004, six (6),
              (B) for the four quarter period ending September 30, 2004, five
                 (5),
              (C) for the four quarter period ending December 31, 2004, five
                 (5),
              (D) for the four quarter period ending March 31, 2005, four (4),
              (E) for the four quarter period ending June 30, 2005, four (4),
              (F) for the four quarter period ending on the last day of any
                 fiscal quarter on and after September 30, 2005, three and one
                 half (3.5); and

              (b) if the Company has failed to provide a timely Borrowing Base
         Certificate in accordance with Section 4.2 on or prior to such day, an
         amount equal to 80% of the Net Borrowing Base in effect on the day
         immediately prior to the date such Borrowing Base Certificate should
         have been delivered to the Agent in accordance with Section 4.2
         hereof.

         (b) Section 9.11(b). Section 9.11(b) is amended and restated in its
entirety as follows:

              (b) The Company shall not permit the ratio of its Financial
         Indebtedness to Adjusted EBITDA at the end of each fiscal quarter,
         calculated for the four quarter period then ended, to exceed (i) 4.00
         to 1.00 for the fiscal quarter ending September 30, 2004, (ii) 4.00 to
         1.00 for the fiscal quarter ending December 31, 2004, (iii) 3.00 to
         1.00 for the fiscal quarter ending March 31, 2005, (iv) 3.00 to 1.00
         for the fiscal quarter ending June 30, 2005, and (v) 2.00 to 1.00 for
         each quarter ending thereafter.

         (c) Section 9.13. Section 9.13 is amended and restated in its entirety
as follows:


                                       2

<PAGE>

              9.13 Fixed Charge Coverage Ratio. The Company shall not permit
         its Fixed Charge Coverage Ratio, calculated at the end of each fiscal
         quarter on and after September 30, 2004 for the four fiscal quarter
         period then ended, to be less than (i) 1.75 to 1.00 for the fiscal
         quarter ending September 30, 2004, (ii) 1.75 to 1.00 for the fiscal
         quarter ending December 31, 2004, (iii) 2.50 to 1.00 for the fiscal
         quarter ending March 31, 2005, (iv) 2.50 to 1.00 for the fiscal
         quarter ending June 30, 2005, and (v) 3.00 to 1.00 for each quarter
         ending thereafter.

         Section 3. Conditions to Effectiveness. This Amendment shall become
effective as of the Amendment Effective Date when the Agent has confirmed (and
have so notified the Company and the Banks) that it has received:

         (i)    counterparts hereof duly executed by the Obligors and the
                Required Banks;

         (ii)   a Certificate of the Company, signed on behalf of the Company
                by its President or Chief Financial Officer, dated as of the
                date hereof, certifying that, after giving effect hereto, the
                following statements shall be true:

                (A) the representations and warranties of each Obligor
         contained in the Credit Documents are correct in all material respects
         on and as of such date (other than those representations and
         warranties that expressly relate solely to a specific earlier date,
         which shall remain correct as of such earlier date), as though made on
         and as of such date; and

                (B) no event has occurred and is continuing which constitutes a
         Default, an Event of Default or both unless waived by this Amendment;

Section 4. Amendment and Ratification. Upon the effectiveness hereof as
provided in the foregoing Section 3, this Amendment shall be deemed to be an
amendment and waiver to the Credit Agreement, and the Credit Agreement, as
modified hereby, is hereby ratified, approved and confirmed to be in full force
and effect in each and every respect. All references to the Credit Agreement in
any other document, instrument, agreement or writing shall hereafter be deemed
to refer to the Credit Agreement as modified hereby.

         Section 5. Governing Law. THIS AMENDMENT AND THE RIGHTS AND
OBLIGATIONS OF THE PARTIES HEREUNDER SHALL BE CONSTRUED IN ACCORDANCE WITH AND
BE GOVERNED BY THE LAWS OF THE STATE OF NEW YORK.

         Section 6. Descriptive Headings, Etc. The descriptive headings of the
several sections of this Amendment are inserted for convenience only and shall
not be deemed to affect the meaning or construction of any of the provisions
hereof.

         Section 7. Counterparts. This Amendment may be executed in any number
of counterparts and by different parties hereto in separate counterparts, each
of which when so executed shall be deemed to be an original and all of which
taken together shall constitute one and the same agreement.


                                       3

<PAGE>

         Section 8. Waiver of Jury Trial. Each of the parties hereto hereby
irrevocably and unconditionally waives, to the fullest extent it may
effectively do so under applicable law, any and all right to trial by jury in
any action or proceeding arising out of or relating to any Loan Document or the
transactions contemplated hereby or thereby.

                  [Remainder of Page Intentionally Left Blank]


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<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to
be duly executed and delivered by their respective duly authorized officers as
of the Amendment Effective Date.

                                     OBLIGORS:

                                     WILLBROS GROUP, INC.

                                     By  /s/ Warren L. Williams
                                         --------------------------------------
                                     Name:  Warren L. Williams
                                     Title: Senior Vice President & Treasurer

                                     WILLBROS U.S.A., INC.

                                     By: /s/ Warren L. Williams
                                         --------------------------------------
                                     Name:  Warren L. Williams
                                            Title: Senior Vice President &
                                                   Treasurer

                                     WILLBROS INTERNATIONAL, INC.

                                     By: /s/ Pamela L. Reiland
                                         --------------------------------------
                                     Name:  Pamela L. Reiland
                                     Title: Treasurer

                                     WILLBROS WEST AFRICA, INC.

                                     By: /s/ Pamela L. Reiland
                                         --------------------------------------
                                     Name:  Pamela L. Reiland
                                     Title: Treasurer

                                     WILLBROS (NIGERIA) LIMITED

                                     By: /s/ J. Kenneth Tillery
                                         --------------------------------------
                                     Name:  J. Kenneth Tillery
                                     Title: Managing Director

                                     WILLBROS (OFFSHORE) NIGERIA LIMITED

                                     By: /s/ J. Kenneth Tillery
                                         --------------------------------------
                                     Name:  J. Kenneth Tillery
                                     Title: Managing Director

                                     WILLBROS MIDDLE EAST, INC.

                                     By: /s/ Pamela L. Reiland
                                         --------------------------------------
                                     Name:  Pamela L. Reiland
                                     Title: Treasurer


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                                     WILLBROS RPI, INC.

                                     By: /s/ Warren L. Williams
                                         --------------------------------------
                                     Name:  Warren L. Williams
                                     Title: Vice President & Treasurer

                                     CONSTRUCTORA CAMSA, C.A.

                                     By: /s/ Warren L. Williams
                                         --------------------------------------
                                     Name:  Warren L. Williams
                                     Title: Principal Director

                                     WILLBROS OPERATING SERVICES, INC.

                                     By: /s/  Kathy E. Alexander
                                         --------------------------------------
                                     Name:  Kathy E. Alexander
                                     Title: Assistant Secretary

                                     WILLBROS ENERGY SERVICES COMPANY

                                     By: /s/ J. Kevin Neal
                                         --------------------------------------
                                     Name:  J. Kevin Neal
                                     Title: President

                                     WILLBROS MARINE ASSETS, INC.

                                     By: /s/ Pamela L. Reiland
                                         --------------------------------------
                                     Name:  Pamela L. Reiland
                                     Title: Treasurer

                                     INTERNATIONAL PIPELINE EQUIPMENT, INC.

                                     By: /s/ Pamela L. Reiland
                                         --------------------------------------
                                     Name:  Pamela L. Reiland
                                     Title: Treasurer


                                     WILLBROS TRANSANDINA S.A.

                                     By: /s/ J. Kenneth Tillery
                                         --------------------------------------
                                     Name:  J. Kenneth Tillery
                                     Title: Managing Director


                                       6

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                                     WILLBROS ENGINEERS, INC.

                                     By: /s/ Warren L. Williams
                                         --------------------------------------
                                     Name:  Warren L. Williams
                                     Title: Treasurer

                                     ESCA EQUIPMENT SERVICE C.A.

                                     By: /s/ Warren L. Williams
                                         --------------------------------------
                                     Name:  Warren L. Williams
                                     Title: Principal Director

                                     WILLBROS MSI CANADA INC.

                                     By: /s/ Warren L. Williams
                                         --------------------------------------
                                     Name:  Warren L. Williams
                                     Title: Vice President & Treasurer

                                     WILLBROS CONSTRUCTORS, INC.

                                     By: /s/ Pamela L. Reiland
                                         --------------------------------------
                                     Name:  Pamela L. Reiland
                                     Title: Treasurer

                                     WILLBROS PACIFIC INDUSTRIAL ELECTRIC,
                                     INC.

                                     By: /s/ Warren L. Williams
                                         --------------------------------------
                                     Name:  Warren L. Williams
                                     Title: Treasurer

                                     WILLBROS PROCESS ENGINEERING DESIGN, INC.

                                     By: /s/ Warren L. Williams
                                         --------------------------------------
                                     Name:  Warren L. Williams
                                     Title: Treasurer


                                       7

<PAGE>

                                     WILLBROS PROCESS ELECTRIC AND CONTROL, INC.

                                     By: /s/ J. Kevin Neal
                                         --------------------------------------
                                     Name:  J. Kevin Neal
                                     Title: President

                                     WILLBROS MT. WEST, INC.

                                     By: /s/ Pamela L. Reiland
                                         --------------------------------------
                                     Name:  Pamela L. Reiland
                                     Title: Vice President & Treasurer


                                       8

<PAGE>

                                     AGENT:

                                     CALYON NEW YORK BRANCH (formerly known as
                                     Credit Lyonnais New York Branch)


                                     By: /s/ Olivier Audemard
                                         --------------------------------------
                                     Name:  Olivier Audemard
                                     Title: Managing Director


                                     ISSUING BANK:

                                     CALYON NEW YORK BRANCH (formerly known as
                                     Credit Lyonnais New York Branch)


                                     By: /s/ Olivier Audemard
                                         --------------------------------------
                                     Name:  Olivier Audemard
                                            Title:   Managing Director


                                     LEAD ARRANGER AND
                                     BOOK RUNNER:

                                     CALYON NEW YORK BRANCH (formerly known as
                                     Credit Lyonnais New York Branch)


                                     By: /s/ Olivier Audemard
                                         --------------------------------------
                                     Name:  Olivier Audemard
                                     Title: Managing Director


                                       9

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                                     SYNDICATION AGENT:

                                     CIBC INC.

                                     By: /s/ John P. Burke
                                         --------------------------------------
                                     Name:  John P. Burke
                                     Title: Executive Director


                                      10

<PAGE>

                                     BANKS:

                                     CALYON NEW YORK BRANCH (formerly known as
                                     Credit Lyonnais New York Branch)


                                     By: /s/ Olivier Audemard
                                         --------------------------------------
                                     Name:  Olivier Audemard
                                     Title: Managing Director


                                      11

<PAGE>

                                     ABU DHABI INTERNATIONAL BANK INC.


                                     By:
                                     Name:
                                     Title:


                                      12

<PAGE>

                                     ARAB BANKING CORPORATION (B.S.C.)


                                     By: /s/ Robert J. Ivosevich
                                         --------------------------------------
                                     Name:  Robert J. Ivosevich
                                     Title: General Manager

                                     By: /s/ Tarek Sherlala
                                         --------------------------------------
                                     Name:  Tarek Sherlala
                                     Title: Vice President


                                      13

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                                     THE BANK OF NOVA SCOTIA


                                     By: /s/ M. D. Smith
                                         --------------------------------------
                                     Name:  M. D. Smith
                                     Title: Agent Operations


                                      14

<PAGE>


                                     BANK OF TEXAS, N.A.

                                     By: /s/ Edward H. Braddock
                                         --------------------------------------
                                     Name:  Edward H. Braddock
                                     Title: Vice President


                                      15

<PAGE>

                                     CIBC INC.


                                     By: /s/ John P. Burke
                                         --------------------------------------
                                     Name:  John P. Burke
                                     Title: Executive Director


                                      16

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                                     COMMERCEBANK, N.A.

                                     By: /s/ Francisco Rivero
                                         --------------------------------------
                                     Name:  Francisco Rivero
                                     Title: Senior Vice President

                                     By: /s/ Lance Shervin Ramesh
                                         --------------------------------------
                                     Name:  Lance Shervin Ramesh
                                     Title: Senior Vice President


                                      17

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                                     COMPASS BANK


                                     By: /s/ Collis Sanders
                                         --------------------------------------
                                     Name:  Collis Sanders
                                     Title: Senior Vice President


                                       18

<PAGE>

                                     JPMORGAN CHASE BANK


                                     By: /s/ Joel J. Landis
                                         --------------------------------------
                                     Name:  Joel J. Landis
                                     Title: Vice President


                                      19

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                                     NATEXIS BANQUES POPULAIRES


                                     By: /s/ Tim Polvado
                                         --------------------------------------
                                     Name:  Tim Polvado
                                     Title: Vice President and Manager


                                     By: /s/ Renaud d/Herbes
\                                        --------------------------------------
                                     Name:  Renaud d'Herbes
                                     Title: Senior Vice President and
                                            Regional Manager


                                      20

<PAGE>


                                      RZB FINANCE, LLC


                                      By: /s/ Astrid Wilke
                                          -------------------------------------
                                      Name:    Astrid Wilke
                                      Title:   President

                                      By: /s/ Eric Salat
                                          -------------------------------------
                                      Name:  Eric Salat
                                      Title: Group Vice President


                                      21

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                                      SOUTHWEST BANK OF TEXAS, NA


                                      By: /s/ C. Ross Bartley
                                          -------------------------------------
                                      Name:  C. Ross Bartley
                                      Title: Vice President


                                      22