Document:

<PAGE>
                                                                 Exhibit 10.22.1

                       FIRST AMENDMENT TO CREDIT AGREEMENT

        This FIRST AMENDMENT TO CREDIT AGREEMENT (this "First Amendment") is
made and entered into effective as of June 1, 2003, between PRIMEENERGY
CORPORATION, a Delaware corporation ("PEC"). PRIMEENERGY MANAGEMENT CORPORATION,
a New York corporation, PRIME OPERATING COMPANY, a Texas corporation, EASTERN
OIL WELL SERVICE COMPANY, a West Virginia corporation, SOUTHWEST OILFIELD
CONSTRUCTION COMPANY, an Oklahoma corporation, and EOWS MIDLAND COMPANY, a Texas
corporation (collectively, the "Borrower"), with each other lender that is a
signatory hereto or becomes a signatory hereto as provided in Section 9.1,
(individually, together with its successors and assigns, a "Lender" and
collectively together, with their respective successors and assigns, the
"Lenders") and GUARANTY BANK, FSB, a federal savings bank, as agent for the
Lenders (in such capacity, together with its successors in such capacity
pursuant to the terms hereof, the "Agent").

                               W I T N E S S E T H

        WHEREAS, the above named parties did execute and exchange counterparts
of that certain Credit Agreement dated December 19, 2002 (the "Agreement"), to
which reference is here made for all purposes;

        WHEREAS, the parties subject to and bound by the Agreement are desirous
of amending the Agreement in the particulars hereinafter set forth;

        NOW, THEREFORE, in consideration of the mutual covenants and agreements
of the parties to the Agreement, as set forth therein, and the mutual covenants
and agreements of the parties hereto, as set forth in this First Amendment, the
parties hereto agree as follows:

                                    ARTICLE I
                                   DEFINITIONS

        1.01 Terms Defined Above. As used herein, each of the terms "Agent."
"Agreement." "Borrower." "First Amendment." and "Lenders" shall have the meaning
assigned to such term hereinabove.

        1.02 Terms Defined in Agreement. As used herein, each term defined in
the Agreement shall have the meaning assigned thereto in the Agreement, unless
expressly provided herein to the contrary.

        1.03 References. References in this First Amendment to Article or
Section numbers shall be to Articles and Sections of this First Amendment,
unless expressly stated herein to the contrary. References in this First
Amendment to "hereby," "herein," hereinafter," hereinabove," "hereinbelow,"
"hereof," and "hereunder" shall be to this First Amendment in its entirety and
not only to the particular Article or Section in which such reference appears.

        1.04 Articles and Sections. This First Amendment, for convenience only,
has been divided into Articles and Sections and it is understood that the
rights, powers, privileges, duties, and other

                                       1
<PAGE>

legal relations of the parties hereto shall be determined from this First
Amendment as an entirety and without regard to such division into Articles and
Sections and without regard to headings prefixed to such Articles and
Sections.

        1.05 Number and Gender. Whenever the context requires, reference herein
made to the single number shall be understood to include the plural and likewise
the plural shall be understood to include the singular. Words denoting sex shall
be construed to include the masculine, feminine, and neuter, when such
construction is appropriate, and specific enumeration shall not exclude the
general, but shall be construed as cumulative. Definitions of terms defined in
the singular and plural shall be equally applicable to the plural or singular,
as the case may be.

                                   ARTICLE II
                                   AMENDMENTS

        The Borrower and the Lender hereby amend the Agreement in the following
particulars:

        2.01 Amendment of Section 1.2. Section 1.2 of the Agreement is hereby
amended as follows:

        The following definition are added to read as follows:

        The definitions of "Term Loan" and "Term Notes" are hereby deleted from
        the Agreement.

        "Reducing Revolving Term Loan" shall mean the Reducing Revolving Term
        Loan described in Section 2.1B.

        "Reducing Revolving Term Loan Available Commitment" shall mean on the
        date of this First Amendment, the sum of $3,599,998. Such amount shall
        reduce by $66,667 per month beginning July 1, 2003.

        "Reducing Revolving Term Loan Balance" shall mean, at any time, the
        outstanding principal balance of the Reducing Revolving Term Notes at
        such time.

        "Reducing Revolving Term Notes" shall mean, collectively, each of the
        promissory notes of the Borrower payable to a Lender in the amount of
        the Reducing Revolving Term Loan Facility Amount of such Lender in the
        form attached hereto as Exhibit I(a) with all blanks in such form
        completed appropriately, together with all renewals, extensions for any
        period, increases, and rearrangements thereof.

        2.02 Amendment of Section 2.1B. Section 2.1B of the Agreement is hereby
amended to read as follows:

        B. Reducing Revolving Term Loan

           (a)    The Reducing Revolving Term Loan shall be in the total amount
                  of $3,599,998, with interest payable monthly by the Borrower
                  to the Lenders beginning on the first day of the month
                  following the month in which borrowings were made under this
                  facility, and continuing on the first day of

                                       2

<PAGE>

                  each calendar month thereafter until the Reducing Revolving
                  Term Loan Balance is zero and/or until December 19, 2004, when
                  all sums owing under this facility are due and payable.

           (b)    The Borrower may only borrow under the Reducing Revolving Term
                  Loan up to the amount of the Reducing Revolving Term Loan
                  Available Commitment. Principal payments of the greater of
                  $66,667 per month or an amount necessary to reduce the
                  Reducing Revolving Term Loan Balance to the Reducing Revolving
                  Term Loan Available Commitment will be required should the
                  amount of borrowings equal to or exceed the Reducing Revolving
                  Term Loan Available Commitment.

           (c)    Upon the terms and conditions (including, without limitation,
                  the right of the Lenders to decline to make any Loan so long
                  as any Default or Event of Default exists) and relying on the
                  representations and warranties contained in this Agreement,
                  each Lender severally agrees, during the Commitment Period, to
                  make Loans, in immediately available funds at the Applicable
                  Lending Office or the Principal Office, to or for the benefit
                  of the Borrower in an aggregate principal amount not to exceed
                  at any time outstanding the lessor of the Facility Amount of
                  such Lender or the Percentage Share of such Lender of the
                  Reducing Revolving Term Loan Balance then in effect. Loans
                  shall be made from time to time on any Business Day designated
                  by the Borrower following receipt by the Agent of a Borrowing
                  Request.

           (d)    Subject to the terms of this Agreement, during the Commitment
                  Period, the Borrower may borrow, repay, and reborrow up to the
                  amount of the Reducing Revolving Term Loan Available
                  Commitment in effect at that time, and convert Loans of one
                  type or with one Interest Period into Loans of another type or
                  with a different Interest Period. Except for prepayments made
                  pursuant to Section 2.10, each borrowing, conversion, and
                  prepayment of principal of Loans shall be in an amount at
                  least equal to $100,000. Each borrowing, prepayment, or
                  conversion of or into a Loan of a different type or, in the
                  case of a LIBO Rate Loan, having a different Interest Period,
                  shall be deemed a separate borrowing, conversion, and
                  prepayment for purposes of the foregoing, one for each type of
                  Loan or Interest Period. Anything in this Agreement to the
                  contrary notwithstanding, the aggregate principal amount of
                  LIBO Rate Loans having the same Interest Period shall be at
                  least equal to $100,000; and if any LIBO Rate Loan would
                  otherwise be in a lesser principal amount for any period, such
                  Loan shall be a Floating Rate Loan during such period.

           (e)    The Loans shall be made and maintained at the Applicable
                  Lending Office or the Principal Office and shall be evidenced
                  by the Notes.

           (f)    Not later than 2:00 p.m., Central Standard or Daylight Savings
                  Time, as the case may be, on the date specified for each
                  borrowing, each Lender shall make available an amount equal to
                  its Percentage Share of the borrowing to

                                       3

<PAGE>

                  be made on such date to the Agent, at an account designated by
                  the Agent, in immediately available funds, for the account of
                  the Borrower. The amount so received by the Agent shall,
                  subject to the terms and conditions hereof, be made available
                  to the Borrower in immediately available funds at the
                  Principal Office by the end of that Business Day. All Loans by
                  each Lender shall be maintained at the Applicable Lending
                  Office of such Lender and shall be evidenced by the Note of
                  such Lender.

           (g)    The failure of any Lender to make any Loan required to be made
                  by it hereunder shall not relieve any other Lender of its
                  obligation to make any Loan required to be made by it, and no
                  Lender shall be responsible for the failure of any other
                  Lender to make any Loan.

        2.03 Amendment of Section 2.12. Section 2.12 of the Agreement is hereby
amended as follows:

        "2.12 Commitment Fee. In addition to interest on the Note as provided
        herein and all other fees payable hereunder and to compensate the Lender
        for maintaining funds available, the Borrower shall pay to the Agent for
        the account of the Lenders, in immediately available funds, on the first
        day of July, 2003, and on the first day of each third calendar month
        thereafter during the Commitment Period, a fee in the amount of .375%
        per annum, calculated on the basis of a year of 365 or 366 days, as the
        case may be, for the actual days elapsed (including the first day but
        excluding the last day), on the average daily amount of the Available
        Commitment and the Reducing Revolving Term Loan Available Commitment
        during the preceding quarterly period."

        2.04 Amendment of Exhibit I(A). Exhibit I(A), as revised, shall be as
attached to this First Amendment.

                                   ARTICLE III
                                   CONDITIONS

        The obligation of the Lenders to amend the Agreement as provided herein
is subject to the fulfillment of the following conditions precedent:

        3.01 Receipt of Documents. The Lender shall have received, reviewed, and
approved the following documents and other items, appropriately executed when
necessary and in form and substance satisfactory to the Lender:

           (a)    multiple counterparts of this First Amendment as requested by
                  the Lender;

           (b)    Reducing Revolving Term Note; and

           (c)    such other agreements, documents, items, instruments,
                  opinions, certificates, waivers, consents, and evidence as the
                  Lender may reasonably request.

                                       4

<PAGE>

        3.02 Accuracy of Representations and Warranties. The representations and
warranties contained in Article IV of the Agreement and this First Amendment
shall be true and correct.

        3.03 Matters Satisfactory to Lenders. All matters incident to the
consummation of the transactions contemplated hereby shall be satisfactory to
the Lenders.

                                   ARTICLE IV
                         REPRESENTATIONS AND WARRANTIES

        The Borrower hereby expressly re-makes, in favor of the Lenders, all of
the representations and warranties set forth in Article IV of the Agreement, and
represents and warrants that all such representations and warranties remain true
and unbreached.

                                    ARTICLE V
                                  RATIFICATION

        Each of the parties hereto does hereby adopt, ratify, and confirm the
Agreement and the other Loan Documents, in all things in accordance with the
terms and provisions thereof, as amended by this First Amendment.

                                   ARTICLE VI
                                 MISCELLANEOUS

        6.01 Scope of Amendment. The scope of this First Amendment is expressly
limited to the matters addressed herein and this First Amendment shall not
operate as a waiver of any past, present, or future breach, Default, or Event of
Default under the Agreement, except to the extent, if any, that any such breach,
Default, or Event of Default is remedied by the effect of this First Amendment.

        6.02 Agreement as Amended. All references to the Agreement in any
document heretofore or hereafter executed in connection with the transactions
contemplated in the Agreement shall be deemed to refer to the Agreement as
amended by this First Amendment.

        6.03 Parties in Interest. All provisions of this First Amendment shall
be binding upon and shall inure to the benefit of the Borrower, the Lender and
their respective successors and assigns.

        6.04 Rights of Third Parties. All provisions herein are imposed solely
and exclusively for the benefit of the Lender and the Borrower, and no other
Person shall have standing to require satisfaction of such provisions in
accordance with their terms and any or all of such provisions may be freely
waived in whole or in part by the Lender at any time if in its sole discretion
it deems it advisable to do so.

        6.05 ENTIRE AGREEMENT. THIS FIRST AMENDMENT CONSTITUTES THE ENTIRE
AGREEMENT BETWEEN THE PARTIES HERETO WITH RESPECT TO THE SUBJECT HEREOF AND
SUPERSEDES ANY PRIOR AGREEMENT, WHETHER WRITTEN OR ORAL, BETWEEN SUCH PARTIES
REGARDING THE SUBJECT HEREOF. FURTHERMORE IN THIS REGARD, THIS FIRST AMENDMENT,
THE AGREEMENT, THE NOTE, THE SECURITY INSTRUMENTS, AND THE OTHER WRITTEN
DOCUMENTS REFERRED TO IN THE AGREEMENT OR EXECUTED IN

                                       5
<PAGE>

CONNECTION WITH OR AS SECURITY FOR THE NOTE REPRESENT, COLLECTIVELY, THE FINAL
AGREEMENT AMONG THE PARTIES THERETO 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.

        6.06 GOVERNING LAW. THIS FIRST AMENDMENT, THE AGREEMENT AND THE NOTE
SHALL BE DEEMED TO BE CONTRACTS MADE UNDER AND SHALL BE CONSTRUED IN ACCORDANCE
WITH AND GOVERNED BY THE LAWS OF THE STATE OF TEXAS. THE PARTIES ACKNOWLEDGE AND
AGREE THAT THIS AGREEMENT AND THE NOTE AND THE TRANSACTIONS CONTEMPLATED HEREBY
BEAR A NORMAL, REASONABLE, AND SUBSTANTIAL RELATIONSHIP TO THE STATE OF TEXAS.

        6.07 JURISDICTION AND VENUE. ALL ACTIONS OR PROCEEDINGS WITH RESPECT TO,
ARISING DIRECTLY OR INDIRECTLY IN CONNECTION WITH, OUT OF, RELATED TO, OR FROM
THIS FIRST AMENDMENT, THE AGREEMENT OR ANY OTHER LOAN DOCUMENT MAY BE LITIGATED
IN COURTS HAVING SITUS IN HARRIS COUNTY, TEXAS. EACH OF THE BORROWER AND THE
LENDER HEREBY SUBMITS TO THE JURISDICTION OF ANY LOCAL, STATE, OR FEDERAL COURT
LOCATED IN HARRIS COUNTY, TEXAS, AND HEREBY WAIVES ANY RIGHTS IT MAY HAVE TO
TRANSFER OR CHANGE THE JURISDICTION OR VENUE OF ANY LITIGATION BROUGHT AGAINST
IT BY THE BORROWER OR THE LENDER IN ACCORDANCE WITH THIS SECTION.

        IN WITNESS WHEREOF, this First Amendment to Credit Agreement is executed
effective the date first hereinabove written.

                                             BORROWER

                                             PRIMEENERGY CORPORATION
                                             PRIMEENERGY MANAGEMENT CORPORATION,
                                             PRIME OPERATING COMPANY, EASTERN
                                             OIL WELL SERVICE COMPANY, SOUTHWEST
                                             OILFIELD CONSTRUCTION COMPANY EOWS
                                             MIDLAND COMPANY

                                             By: /s/ Beverly A.  Cummings
                                                 -------------------------------
                                                      Beverly A.  Cummings
                                                      Executive Vice President,
                                                      Treasurer, and
                                                      Chief Financial Officer

                                       6

<PAGE>

                                            AGENT AND LENDER

                                            GUARANTY BANK, FSB

                                             By: /s/ Richard E. Menchaca
                                                 -------------------------------
                                                     Richard E. Menchaca
                                                     Senior Vice President

                                       7

<PAGE>

                                  EXHIBIT I(A)
                  [FORM OF REDUCING REVOLVING TERM NOTE]

                             REDUCING REVOLVING TERM
                                PROMISSORY NOTE
$3,599,998                      Houston, Texas                       June 1,2003

        FOR VALUE RECEIVED and WITHOUT GRACE, the undersigned ("Maker") promises
to pay to the order of GUARANTY BANK, FSB ("Payee"), at its banking quarters in
Houston, Harris County, Texas, the sum of THREE MILLION, FIVE HUNDRED AND
NINETY-NINE THOUSAND, NINE HUNDRED AND NINETY-EIGHT DOLLARS ($3,599,998), or so
much thereof as may be advanced against this Note pursuant to the Credit
Agreement dated of even date herewith by and between Maker and Payee (as
amended, restated, or supplemented from time to time, the "Credit Agreement"),
together with interest at the rates and calculated as provided in the Credit
Agreement.

        Reference is hereby made to the Credit Agreement for matters governed
thereby, including, without limitation, certain events which will entitle the
holder hereof to accelerate the maturity of all amounts due hereunder.
Capitalized terms used but not defined in this Note shall have the meanings
assigned to such terms in the Credit Agreement.

        This Note is issued pursuant to, is the "Note" under, and is payable as
provided in the Credit Agreement. Subject to compliance with applicable
provisions of the Credit Agreement, Maker may at any time pay the full amount or
any part of this Note without the payment of any premium or fee, but such
payment shall not, until this Note is fully paid and satisfied, excuse the
payment as it becomes due of any payment on this Note provided for in the Credit
Agreement.

        Without being limited thereto or thereby, this Note is secured by the
Security Instruments.

        THIS NOTE SHALL BE GOVERNED AND CONTROLLED BY THE LAWS OF THE STATE OF
TEXAS WITHOUT GIVING EFFECT TO PRINCIPLES THEREOF RELATING TO CONFLICTS OF LAW;
PROVIDED, HOWEVER, THAT CHAPTER 345 OF THE TEXAS FINANCE CODE (WHICH REGULATES
CERTAIN REVOLVING CREDIT LOAN ACCOUNTS AND REVOLVING TRIPARTY ACCOUNTS) SHALL
NOT APPLY TO THIS NOTE.

                           (PAGE ONE OF TWO PAGE NOTE)

                                       ii

<PAGE>

                                             PRIMEENERGY CORPORATION PRIMEENERGY
                                             MANAGEMENT CORPORATION, PRIME
                                             OPERATING COMPANY, EASTERN OIL WELL
                                             SERVICE COMPANY, SOUTHWEST OILFIELD
                                             CONSTRUCTION COMPANY
                                             EOWS MIDLAND COMPANY

                                             By: /s/ Beverly A. Cummings
                                                --------------------------------
                                                  Beverly A. Cummings
                                                  Executive Vice President,
                                                  Treasurer, and Chief Financial
                                                  Officer

                                      iii

<PAGE>

                             REDUCING REVOLVING TERM
                                PROMISSORY NOTE

$3,599,998                      Houston, Texas                      June 1, 2003

        FOR VALUE RECEIVED and WITHOUT GRACE, the undersigned ("Maker") promises
to pay to the order of GUARANTY BANK, FSB ("Payee"), at its banking quarters in
Houston, Harris County, Texas, the sum of THREE MILLION, FIVE HUNDRED AND
NINETY-NINE THOUSAND, NINE HUNDRED AND NINETY-EIGHT DOLLARS ($3,599,998), or so
much thereof as may be advanced against this Note pursuant to the Credit
Agreement dated of even date herewith by and between Maker and Payee (as
amended, restated, or supplemented from time to time, the "Credit Agreement"),
together with interest at the rates and calculated as provided in the Credit
Agreement.

        Reference is hereby made to the Credit Agreement for matters governed
thereby, including, without limitation, certain events which will entitle the
holder hereof to accelerate the maturity of all amounts due hereunder.
Capitalized terms used but not defined in this Note shall have the meanings
assigned to such terms in the Credit Agreement.

        This Note is issued pursuant to, is the "Note" under, and is payable as
provided in the Credit Agreement. Subject to compliance with applicable
provisions of the Credit Agreement, Maker may at any time pay the full amount or
any part of this Note without the payment of any premium or fee, but such
payment shall not, until this Note is fully paid and satisfied, excuse the
payment as it becomes due of any payment on this Note provided for in the Credit
Agreement.

        Without being limited thereto or thereby, this Note is secured by the
Security Instruments.

        THIS NOTE SHALL BE GOVERNED AND CONTROLLED BY THE LAWS OF THE STATE OF
TEXAS WITHOUT GIVING EFFECT TO PRINCIPLES THEREOF RELATING TO CONFLICTS OF LAW;
PROVIDED, HOWEVER, THAT CHAPTER 345 OF THE TEXAS FINANCE CODE (WHICH REGULATES
CERTAIN REVOLVING CREDIT LOAN ACCOUNTS AND REVOLVING TRIPARTY ACCOUNTS) SHALL
NOT APPLY TO THIS NOTE.

                           (PAGE ONE OF TWO PAGE NOTE)

<PAGE>

                                             PRIMEENERGY CORPORATION PRIMEENERGY
                                             MANAGEMENT CORPORATION, PRIME
                                             OPERATING COMPANY, EASTERN OIL WELL
                                             SERVICE COMPANY, SOUTHWEST OILFIELD
                                             CONSTRUCTION COMPANY
                                             EOWS MIDLAND COMPANY

                                             By: /s/ Beverly A. Cummings
                                                --------------------------------
                                                  Beverly A. Cummings
                                                  Executive Vice President,
                                                  Treasurer, and Chief Financial
                                                  Officer<PAGE>
                                                                 Exhibit 10.22.2

                      SECOND AMENDMENT TO CREDIT AGREEMENT

                                     BETWEEN

                             PRIMEENERGY CORPORATION
                       PRIMEENERGY MANAGEMENT CORPORATION
                             PRIME OPERATING COMPANY
                        EASTERN OIL WELL SERVICE COMPANY
                     SOUTHWEST OILFIELD CONSTRUCTION COMPANY
                              EOWS MIDLAND COMPANY
                           F-W OIL EXPLORATION L.L.C.

                                       AND

                          GUARANTY BANK, FSB, AS AGENT
                                  AND A LENDER

                       EFFECTIVE AS OF SEPTEMBER 22, 2003

             REDUCING REVOLVING LINE OF CREDIT OF UP TO $50,000,000
                   REDUCING REVOLVING TERM LOAN OF $3,666,665

<PAGE>

                                  TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                         PAGE
                                                                                         ----
<S>                                                                                      <C>
ARTICLE I       DEFINITIONS.........................................................      1
  1.01          Terms Defined Above.................................................      1
  1.02          Terms Defined in Agreement..........................................      1
  1.03          References..........................................................      1
  1.04          Articles and Sections...............................................      2
  1.05          Number and Gender...................................................      2
ARTICLE II      AMENDMENTS..........................................................      2
  2.01          Amendment of Section 2.9(a).........................................      2
  2.02          Addition of Section 2.25............................................      2
  2.03          Amendment of Section 6.6............................................      2
  2.04          Amendment of Section 6.7............................................      2
  2.05          Amendment of Section 6.8............................................      3
ARTICLE III     CONDITIONS..........................................................      3
  3.01          Receipt of Documents................................................      3
  3.02          Accuracy of Representations and Warranties..........................      4
  3.03          Matters Satisfactory to Lenders.....................................      4
ARTICLE IV      REPRESENTATIONS AND WARRANTIES......................................      4
ARTICLE V       RATIFICATION........................................................      5
ARTICLE VI      MISCELLANEOUS.......................................................      5
  6.01          Scope of Amendment..................................................      5
  6.02          Agreement as Amended................................................      5
  6.03          Parties in Interest.................................................      5
  6.04          Rights of Third Parties.............................................      5
  6.05          ENTIRE AGREEMENT....................................................      5
  6.06          GOVERNING LAW.......................................................      5
  6.07          JURISDICTION AND VENUE..............................................      6
</TABLE>

                                       i

<PAGE>

                      SECOND AMENDMENT TO CREDIT AGREEMENT

        This SECOND AMENDMENT TO CREDIT AGREEMENT (this "Second Amendment") is
made and entered into effective as of September 22, 2003, between PRIMEENERGY
CORPORATION, a Delaware corporation ("PEC"), PRIMEENERGY MANAGEMENT CORPORATION,
a New York corporation, PRIME OPERATING COMPANY, a Texas corporation, EASTERN
OIL WELL SERVICE COMPANY, a West Virginia corporation, SOUTHWEST OILFIELD
CONSTRUCTION COMPANY, an Oklahoma corporation, EOWS MIDLAND COMPANY, a Texas
corporation, and F-W OIL EXPLORATION L.L.C., a Delaware limited liability
company ("FWOE") (collectively, the "Borrower"), with each other lender that is
a signatory hereto or becomes a signatory hereto as provided in Section 9.1,
(individually, together with its successors and assigns, a "'Lender" and
collectively together, with their respective successors and assigns, the
"Lenders") and GUARANTY BANK, FSB, a federal savings bank, as agent for the
Lenders (in such capacity, together with its successors in such capacity
pursuant to the terms hereof, the "Agent").

                               W I T N E S S E T H

        WHEREAS, the above named parties did execute and exchange counterparts
of that certain Credit Agreement dated December 19, 2002, as amended by First
Amendment to Credit Agreement dated effective as of June 1, 2003 (the
"Agreement"), to which reference is here made for all purposes;

        WHEREAS, Borrower has acquired a majority interest in FWOE and FWOE has
been added to the Agreement as a Borrower effective the date of this Second
Amendment;

        WHEREAS, the parties subject to and bound by the Agreement are desirous
of amending the Agreement in the particulars hereinafter set forth;

        NOW, THEREFORE, in consideration of the mutual covenants and agreements
of the parties to the Agreement, as set forth therein, and the mutual covenants
and agreements of the parties hereto, as set forth in this Second Amendment, the
parties hereto agree as follows:

                                    ARTICLE I
                                  DEFINITIONS

        1.01 Terms Defined Above. As used herein, each of the terms "Agent,"
"Agreement," "Borrower," "Lenders" and "Second Amendment." shall have the
meaning assigned to such term hereinabove.

        1.02 Terms Defined in Agreement. As used herein, each term defined in
the Agreement shall have the meaning assigned thereto in the Agreement, unless
expressly provided herein to the contrary.

        1.03 References. References in this Second Amendment to Article or
Section numbers shall be to Articles and Sections of this Second Amendment,
unless expressly stated herein to the contrary. References in this Second
Amendment to "hereby," "herein," hereinafter," hereinabove,"

                                       1
<PAGE>

"hereinbelow," "hereof." and "hereunder" shall be to this Second Amendment in
its entirety and not only to the particular Article or Section in which such
reference appears.

        1.04 Articles and Sections. This Second Amendment, for convenience only,
has been divided into Articles and Sections and it is understood that the
rights, powers, privileges, duties, and other legal relations of the parties
hereto shall be determined from this Second Amendment as an entirety and without
regard to such division into Articles and Sections and without regard to
headings prefixed to such Articles and Sections.

        1.05 Number and Gender. Whenever the context requires, reference herein
made to the single number shall be understood to include the plural and likewise
the plural shall be understood to include the singular. Words denoting sex shall
be construed to include the masculine, feminine, and neuter, when such
construction is appropriate, and specific enumeration shall not exclude the
general, but shall be construed as cumulative. Definitions of terms defined in
the singular and plural shall be equally applicable to the plural or singular,
as the case may be.

                                   ARTICLE II
                                   AMENDMENTS

        The Borrower and the Lender hereby amend the Agreement in the following
particulars:

        2.01 Amendment of Section 2.9(a). Section 2.9(a) of the Agreement is
hereby amended to read as follows:

        "2.9 Borrowing Base Determinations, (a) The Borrowing Base as of
        September 9, 2003, is acknowledged by the Borrower and the Lenders to be
        $25,800,000."

        2.02 Addition of Section 2.25. Section 2.25 is added to the Agreement
        as follows:

        "2.25 Limitation of Liability of FWOE. FWOE's liability to the Lender on
        the Note and other Obligations under the Agreement is limited to
        $3,800,000."

        2.03 Amendment of Section 6.6. Section 6.6 of the Agreement shall be
        amended to add the following sentence:

        "6.6 Loans or Advances. ... Notwithstanding the above, the Borrower may
        make a loan to FWOE in the amount of $1,312,500 pursuant to the terms of
        the Subscription Agreement dated August 27, 2003, by and between FWOE,
        F-W Oil Interests, Inc., Frank C. Wade and PEC."

        2.04 Amendment of Section 6.7. Section 6.7 of the Agreement shall be
amended to add the following sentence:

        "6.7 Investments. ... Notwithstanding the above, the Borrower may make
        an investment in FWOE in the amount of $4,166,000 pursuant to the terms
        of the Subscription Agreement dated August 27, 2003, by and between
        FWOE, F-W Oil Interests, Inc., Frank C. Wade and PEC."

                                       2

<PAGE>

        2.05 Amendment of Section, 6.8. Section 6.8 of the Agreement shall be
amended to add the following sentence:

        "6.8 Dividends and Distributions. ... Notwithstanding the above, FWOE
        may make distributions to PEC (1) in the amount of $2,187,500, and (2)
        in the amount of $1,312,500 in payment of the Promissory Note dated
        August 27, 2003 and (3) to F-W Oil Interests, Inc. and Frank C. Wade in
        amounts due in settlement of accounting matters as a result of the
        Subscription Agreement dated August 27, 2003, between PEC and FWOE et
        al."

                                  ARTICLE III
                                   CONDITIONS

        The obligation of the Lenders to amend the Agreement as provided herein
 is subject to the fulfillment of the following conditions precedent:

        3.01 Receipt of Documents. The Lender shall have received, reviewed, and
approved the following documents and other items, appropriately executed when
necessary and in form and substance satisfactory to the Lender:

        (a)      multiple counterparts of this Second Amendment as requested by
                 the Lender;

        (b)      Mortgage, Deed of Trust, Indenture, Security Agreement.
                 Assignment of Production and Financing Statement from FWOE
                 covering all Oil and Gas Properties of FWOE and all
                 improvements, personal property, and fixtures related thereto;

        (c)      Financing Statements from FWOE, as debtor, constituent to the
                 instrument described in clause (b) above;

        (d)      undated letters, in form and substance satisfactory to the
                 Agent, from FWOE to each purchaser of production and disburser
                 of the proceeds of production from or attributable to the
                 Mortgaged Properties, together with additional letters with the
                 addressees left blank, authorizing and directing the addressees
                 to make future payments attributable to production from the
                 Mortgaged Properties directly to the Agent;

        (e)      Security Agreement from FWOE pledging contract rights, etc.;

        (f)      Financing Statements from FWOE, as debtor, constituent to the
                 instrument described in clause (e) above;

        (g)      payment by FWOE to Guaranty Bank, FSB of $19,000 as a Facility
                 Fee for the increase in the Borrowing Base of $3,800,000;

        (h)      Ratification of and Amendment to Mortgage, Deed of Trust,
                 Indenture, Security Agreement, Financing Statement and
                 Assignment of Production;

                                       3

<PAGE>

        (i)      Financing Statements from the Borrower, as debtor, constituent
                 to the instrument described in clause (h) above;

        (j)      pledge of membership interest of Borrower in FWOE together with
                 blank power of sale;

        (k)      copies of the formation documents of FWOE and all amendments
                 thereto, accompanied by a certificate dated the Closing Date
                 issued by the secretary or an assistant secretary or another
                 authorized representative of FWOE to the effect that each such
                 copy is correct and complete;

        (l)      a certificate of incumbency dated the Closing Date, including
                 specimen signatures of all officers or other representatives of
                 FWOE who are authorized to execute Loan Documents on behalf of
                 FWOE, such certificate being executed by an authorized
                 representative of FWOE;

        (m)      copies of resolutions of FWOE, adopted by the board of managers
                 of FWOE approving the Loan Documents to which FWOE is a party
                 and authorizing the transactions contemplated herein and
                 therein, accompanied by a certificate dated the date of the
                 Second Amendment issued by an authorized representative of FWOE
                 to the effect that such copies are true and correct copies of
                 resolutions duly adopted and that such resolutions constitute
                 all the resolutions adopted with respect to such transactions,
                 have not been amended, modified, or rescinded in any respect,
                 and are in full force and effect as of the date of such
                 certificate;

        (n)      Note in the form of Exhibit I hereto; and

        (o)      such other agreements, documents, items, instruments, opinions,
                 certificates, waivers, consents, and evidence as the Agent may
                 reasonably request.

        3.02 Accuracy of Representations and Warranties. The representations and
warranties contained in Article IV of the Agreement and this Second Amendment
shall be true and correct.

        3.03 Matters Satisfactory to Lenders. All matters incident to the
consummation of the transactions contemplated hereby shall be satisfactory to
the Lenders.

        3.04 Amendment of Exhibit I. Exhibit I, i.e. the Form of Promissory
Note, shall be as set forth on Exhibit I to this Second Amendment.

                                   ARTICLE IV
                         REPRESENTATIONS AND WARRANTIES

        The Borrower hereby expressly re-makes, in favor of the Lenders, all of
the representations and warranties set forth in Article IV of the Agreement, and
represents and warrants that all such representations and warranties remain true
and unbreached.

                                       4

<PAGE>

                                    ARTICLE V
                                  RATIFICATION

        Each of the parties hereto does hereby adopt, ratify, and confirm the
Agreement and the other Loan Documents, in all things in accordance with the
terms and provisions thereof, as amended by this Second Amendment.

                                   ARTICLE VI
                                  MISCELLANEOUS

        6.01 Scope of Amendment. The scope of this Second Amendment is expressly
limited to the matters addressed herein and this Second Amendment shall not
operate as a waiver of any past, present, or future breach, Default, or Event of
Default under the Agreement, except to the extent, if any, that any such breach,
Default, or Event of Default is remedied by the effect of this Second Amendment.

        6.02 Agreement as Amended. All references to the Agreement in any
document heretofore or hereafter executed in connection with the transactions
contemplated in the Agreement shall be deemed to refer to the Agreement as
amended by this Second Amendment.

        6.03 Parties in Interest. All provisions of this Second Amendment shall
be binding upon and shall inure to the benefit of the Borrower, the Lender and
their respective successors and assigns.

        6.04 Rights of Third Parties. All provisions herein are imposed solely
and exclusively for the benefit of the Lender and the Borrower, and no other
Person shall have standing to require satisfaction of such provisions in
accordance with their terms and any or all of such provisions may be freely
waived in whole or in part by the Lender at any time if in its sole discretion
it deems it advisable to do so.

        6.05 ENTIRE AGREEMENT. THIS SECOND AMENDMENT CONSTITUTES THE ENTIRE
AGREEMENT BETWEEN THE PARTIES HERETO WITH RESPECT TO THE SUBJECT HEREOF AND
SUPERSEDES ANY PRIOR AGREEMENT, WHETHER WRITTEN OR ORAL, BETWEEN SUCH PARTIES
REGARDING THE SUBJECT HEREOF. FURTHERMORE IN THIS REGARD, THIS SECOND AMENDMENT,
THE AGREEMENT, THE NOTE, THE SECURITY INSTRUMENTS, AND THE OTHER WRITTEN
DOCUMENTS REFERRED TO IN THE AGREEMENT OR EXECUTED IN CONNECTION WITH OR AS
SECURITY FOR THE NOTE REPRESENT, COLLECTIVELY, THE FINAL AGREEMENT AMONG THE
PARTIES THERETO 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.

        6.06 GOVERNING LAW. THIS SECOND AMENDMENT, THE AGREEMENT AND THE NOTE
SHALL BE DEEMED TO BE CONTRACTS MADE UNDER AND SHALL BE CONSTRUED IN ACCORDANCE
WITH AND GOVERNED BY THE LAWS OF THE STATE OF TEXAS. THE PARTIES ACKNOWLEDGE AND
AGREE THAT THIS AGREEMENT AND THE NOTE AND THE TRANSACTIONS CONTEMPLATED

                                       5

<PAGE>

HEREBY BEAR A NORMAL, REASONABLE, AND SUBSTANTIAL RELATIONSHIP TO THE STATE OF
TEXAS.

        6.07 JURISDICTION AND VENUE. ALL ACTIONS OR PROCEEDINGS WITH RESPECT TO,
ARISING DIRECTLY OR INDIRECTLY IN CONNECTION WITH, OUT OF, RELATED TO, OR FROM
THIS SECOND AMENDMENT, THE AGREEMENT OR ANY OTHER LOAN DOCUMENT MAY BE LITIGATED
IN COURTS HAVING SITUS IN HARRIS COUNTY, TEXAS. EACH OF THE BORROWER AND THE
LENDER HEREBY SUBMITS TO THE JURISDICTION OF ANY LOCAL, STATE, OR FEDERAL COURT
LOCATED IN HARRIS COUNTY, TEXAS, AND HEREBY WAIVES ANY RIGHTS IT MAY HAVE TO
TRANSFER OR CHANGE THE JURISDICTION OR VENUE OF ANY LITIGATION BROUGHT AGAINST
IT BY THE BORROWER OR THE LENDER IN ACCORDANCE WITH THIS SECTION.

                  (REMAINDER OF PAGE INTENTIONALLY LEFT BLANK)

                                       6

<PAGE>

        IN WITNESS WHEREOF, this Second Amendment to Credit Agreement is
executed effective the date first hereinabove written.

                                             BORROWER

                                             PRIMEENERGY CORPORATION PRIMEENERGY
                                             MANAGEMENT CORPORATION, PRIME
                                             OPERATING COMPANY, EASTERN OIL WELL
                                             SERVICE COMPANY, SOUTHWEST OILFIELD
                                             CONSTRUCTION COMPANY EOWS MIDLAND
                                             COMPANY

                                             By:
                                                --------------------------------
                                                    Beverly A. Cummings
                                                    Executive Vice President,
                                                    Treasurer, and Chief
                                                    Financial Officer

                                             F-W OIL EXPLORATION L.L.C.

                                             By:
                                                --------------------------------
                                                    Jim R. Brock
                                                    President and CFO

                                       7

<PAGE>

                                             AGENT AND LENDER

                                             GUARANTY BANK, FSB

                                             By:
                                                --------------------------------
                                                     Richard E. Menchaca
                                                     Senior Vice President

                                       8

<PAGE>

                                   EXHIBIT I
                                 [FORM OF NOTE]

                                PROMISSORY NOTE

$50,000,000                      Houston, Texas                September 22,2003

        FOR VALUE RECEIVED and WITHOUT GRACE, the undersigned ("Maker") promises
to pay to the order of GUARANTY BANK, FSB ("Payee"), at its banking quarters in
Houston, Harris County, Texas, the sum of FIFTY MILLION DOLLARS ($50,000,000),
or so much thereof as may be advanced against this Note pursuant to the Credit
Agreement dated of even date herewith by and between Maker and Payee (as
amended, restated, or supplemented from time to time, the "Credit Agreement"),
together with interest at the rates and calculated as provided in the Credit
Agreement.

        Reference is hereby made to the Credit Agreement for matters governed
thereby, including, without limitation, certain events which will entitle the
holder hereof to accelerate the maturity of all amounts due hereunder.
Capitalized terms used but not defined in this Note shall have the meanings
assigned to such terms in the Credit Agreement.

        This Note is issued pursuant to, is the "Note" under, and is payable as
provided in the Credit Agreement. Subject to compliance with applicable
provisions of the Credit Agreement, Maker may at any time pay the full amount or
any part of this Note without the payment of any premium or fee, but such
payment shall not, until this Note is fully paid and satisfied, excuse the
payment as it becomes due of any payment on this Note provided for in the Credit
Agreement.

        Without being limited thereto or thereby, this Note is secured by the
Security Instruments.

        THIS NOTE SHALL BE GOVERNED AND CONTROLLED BY THE LAWS OF THE STATE OF
TEXAS WITHOUT GIVING EFFECT TO PRINCIPLES THEREOF RELATING TO CONFLICTS OF LAW;
PROVIDED, HOWEVER, THAT CHAPTER 345 OF THE TEXAS FINANCE CODE (WHICH REGULATES
CERTAIN REVOLVING CREDIT LOAN ACCOUNTS AND REVOLVING TRIPARTY ACCOUNTS) SHALL
NOT APPLY TO THIS NOTE.

                           (PAGE ONE OF TWO PAGE NOTE)

<PAGE>

                                             PRIMEENERGY CORPORATION
                                             PRIMEENERGY MANAGEMENT CORPORATION,
                                             PRIME OPERATING COMPANY, EASTERN
                                             OIL WELL SERVICE COMPANY, SOUTHWEST
                                             OILFIELD CONSTRUCTION COMPANY EOWS
                                             MIDLAND COMPANY

                                             By:
                                                --------------------------------
                                                    Beverly A. Cummings
                                                    Executive Vice President,
                                                    Treasurer, and Chief
                                                    Financial Officer

                                             F-W OIL EXPLORATION L.L.C.

                                             By:
                                                --------------------------------
                                                    Jim R. Brock
                                                    President and CFO

                          (PAGE TWO OF TWO PAGE NOTE)

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