Document:

<PAGE>
                                                               EXHIBIT 10.22.3

ATTORNEYS & COUNSELORS
1401 McKinney Street, Suite 1900                               Donna Lyn Carter
Houston, Texas 77010                        [JW LOGO]          (713)752-4217
(713) 752-4200 - fax (713) 752-4221                            dcarter@jw.com
www.jw.com                            JACKSON WALKER L.L.P.

                                         March 19, 2004

      VIA FEDERAL EXPRESS

      Mr. Dan Solomon
      Guaranty Bank, FSB
      8333 Douglas Avenue
      Dallas, Texas 75225

            Re:   Guaranty Bank, FSB/PrimeEnergy Corporation Credit Facility
                  (Our File No. 120117.00012)

      Dear Dan:

            As we discussed, enclosed is a counterpart original Third Amendment
      to Credit Agreement dated effective February 17, 2004, between PrimeEnergy
      Corporation, PrimeEnergy Management Corporation, PrimeEnergy 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.

            Please acknowledge receipt of the above referenced document by
      signing the enclosed copy of this letter and returning it to me in the
      enclosed postage paid envelope.

                                            Very truly yours,

                                            /s/ Donna L. Carter
                                            Donna L. Carter
                                            Paralegal/Transactions

      DLC/cmj
      Enclosures
      cc:  Ms. Beverly Cummings (w/ encl.)

           Wayne G. Dotson (Firm)

      Receipt of the above referenced document is acknowledged this ___ day of
      March, 2004.

Austin                               ___________________________________________
Dallas                               Dan Solomon, Guaranty Bank, FSB
Fort Worth
Houston
Richardson
San Angelo                           ___________________________________________
San Antonio                          Beverly Cummings, PrimeEnergy Corporation

Member of GLOBALAW(TM)

<PAGE>

Delivery Ticket                                                      Page 1 of 1

Last step: Please print this page as the delivery ticket for the courier.

[HOUSTON EXPRESS LOGO]

Houston Express Couriers, Inc.
P.O. Box 70349
Houston, Texas 77270
Phone Number: 713-869-0100

CUSTOMER: Jackson Walker Law Firm
DATE: 3/19/2004
TICKET NUMBER: W59150
TYPE OF DELIVERY: Super Express (A.S.A.P.)

<TABLE>
<CAPTION>
                             Shipper                                                   Consignee
<S>                          <C>                               <C>                <C>
COMPANY                      Jackson Walker Law Firm           COMPANY            PrimeEnergy
                                                                                  Corporation
ADDRESS LINE 1               1401 McKinney Street, Suite       ADDRESS LINE       2900 Wilcrest Drive
                             1900                              1
ADDRESS LINE 2                                                 ADDRESS LINE
                                                               2                  Suite 475
CITY, STATE, ZIP             Houston, TX 77010                 CITY, STATE, ZIP   Houston, TX 77042
ATTENTION                    Cynthia John                      ATTENTION          Beverly Cummings
PHONE                        713-752-4200 ext. 4325            PHONE              713-735-0000

RETURN SERVICE               NO                                NIGHT SERVICE      No
LEAVE WITHOUT                NO                                NO. PIECES         1
SIGNATURE
DESCRIPTION                                                    C-M #              120117.00012
BILLING ID                   120117.00012
ENTERED BY                   Cynthia John
SPECIAL INSTRUCTIONS
TRACKING INFORMATION
</TABLE>

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<PAGE>

--------------------------------------------------------------------------------

                       THIRD 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 FEBRUARY 17, 2004

                        ---------------------------------

             REDUCING REVOLVING LINE OF CREDIT OF UP TO $50,000,000
                   REDUCING REVOLVING TERM LOAN OF $3,599,998

                        ---------------------------------

--------------------------------------------------------------------------------
<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 1.2 .............................         2
  2.02      Amendment of Section 2.9 .............................         2
ARTICLE III CONDITIONS ...........................................         3
  3.01      Receipt of Documents .................................         3
  3.02      Accuracy of Representations and Warranties ...........         3
  3.03      Matters Satisfactory to Lenders ......................         3
ARTICLE IV  REPRESENTATIONS AND WARRANTIES .......................         3
ARTICLE V   RATIFICATION .........................................         4
ARTICLE VI  MISCELLANEOUS ........................................         4
  6.01      Scope of Amendment ...................................         4
  6.02      Agreement as Amended .................................         4
  6.03      Parties in Interest ..................................         4
  6.04      Rights of Third Parties ..............................         4
  6.05      ENTIRE AGREEMENT .....................................         4
  6.06      GOVERNING LAW ........................................         4
  6.07      JURISDICTION AND VENUE ...............................         5
</TABLE>

<PAGE>

                       THIRD AMENDMENT TO CREDIT AGREEMENT

      This THIRD AMENDMENT TO CREDIT AGREEMENT (this "Third Amendment") is made
and entered into effective as of February 17, 2004, 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, and as further
amended by Second Amendment to Credit Agreement dated effective as of September
22,2003 (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 Third 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 "Third 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 Third Amendment to Article or Section
numbers shall be to Articles and Sections of this Third Amendment, unless
expressly stated herein to the contrary. References in this Third Amendment to
"hereby," "herein," hereinafter," hereinabove," "hereinbelow," "hereof," and
"hereunder" shall be to this Third Amendment in its entirety and not only to the
particular Article or Section in which such reference appears.

                                       1
<PAGE>

      1.04 Articles and Sections. This Third 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 Third 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 definitions shall be added and/or amended to read as
      follows:

      "Commitment Termination Date" shall mean March 31,2007.

      "Final Maturity" shall mean March 31, 2007.

      2.02 Amendment of Section 2.9(a). Section 2.9(a) of the Agreement shall be
amended to read as follows:

      "2.9 Borrowing Base Determinations, (a) The Borrowing Base as of February
      17, 2003, is acknowledged by the Borrower and the Lenders to be
      $44,000,000."

      2.03 Addition of Section 2.9(e). Section 2.9(e) is added to the Agreement
      to read as follows:

      "2.9 Borrowing Base Determinations.---(e) The Borrowing Base may be
      decreased by the Borrower by giving the Agent written notice of the amount
      of the decrease and the resulting Borrowing Base. The Borrower may then
      only borrow up to the amount of the decreased Borrowing Base and if any
      future increase in the Borrowing Base is required the Borrower shall
      furnish the Agent with the information requested by the Agreement as set
      forth in (b) above and pay all fees required by increasing the Borrowing
      Base."

      2.04 Amendment of Section 2.25. Section 2.25 of the Agreement is amended
      to read as follows:

                                       2
<PAGE>

      "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
      $10,120,000.00."

      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
      repay advances made by PEC in the amount of $1,275,000.00 and by Frank C.
      Wade in the amount of $847,260.00."

                                   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 Agent 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 Third Amendment as requested by the
            Agent.

      (b)   payment by Borrower to Guaranty Bank, FSB of $165,000 as an
            extension fee;

      (c)   payment by Borrower to Guaranty Bank, FSB of $91,000 as a Facility
            Fee for the increase in the Borrowing Base; and

      (d)   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 Third 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.

                                        3

<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 Third Amendment.

                                   ARTICLE VI
                                  MISCELLANEOUS

      6.01   Scope of Amendment. The scope of this Third Amendment is expressly
limited to the matters addressed herein and this Third 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 Third 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 Third Amendment.

      6.03   Parties in Interest. All provisions of this Third 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 THIRD 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 THIRD 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 THIRD 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

                                        4

<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 THIRD 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)

                                        5

<PAGE>

      IN WITNESS WHEREOF, this Third 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

                               F-W OIL EXPLORATION L.L.C.

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

                                        6

<PAGE>

                               AGENT AND LENDER

                               GUARANTY BANK, FSB

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

                                       7<PAGE>

                                                                 EXHIBIT 10.22.4

================================================================================

                      FOURTH 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

                                      AND

                          GUARANTY BANK, FSB, AS AGENT
                                  AND A LENDER

                       EFFECTIVE AS OF DECEMBER 28, 2004

                       ---------------------------------

             REDUCING REVOLVING LINE OF CREDIT OF UP TO $50,000,000
                   REDUCING REVOLVING TERM LOAN OF $3,599,998

                       ---------------------------------

================================================================================

<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 1.2....................    2
    2.02       Amendment of Section 2.9....................    2
ARTICLE III    CONDITIONS..................................    2
    3.01       Receipt of Documents........................    2
    3.02       Accuracy of Representations and Warranties..    3
    3.03       Matters Satisfactory to Lenders.............    3
 ARTICLE IV    REPRESENTATIONS AND WARRANTIES..............    3
 ARTICLE V     RATIFICATION................................    3
 ARTICLE VI    MISCELLANEOUS...............................    3
    6.01       Scope of Amendment..........................    3
    6.02       Agreement as Amended........................    3
    6.03       Parties in Interest.........................    3
    6.04       Rights of Fourth Parties....................    3
    6.05       ENTIRE AGREEMENT............................    3
    6.06       GOVERNING LAW...............................    4
    6.07       JURISDICTION AND VENUE......................    4
</TABLE>

<PAGE>

                      FOURTH AMENDMENT TO CREDIT AGREEMENT

      This FOURTH AMENDMENT TO CREDIT AGREEMENT (this "Fourth Amendment") is
made and entered into effective as of December 28, 2004, 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, as amended by First
Amendment to Credit Agreement dated effective as of June 1, 2003, as further
amended by Second Amendment to Credit Agreement dated effective as of September
22, 2003, and as further amended by Third Amendment to Credit Agreement dated
effective as of February 17, 2004 (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 Fourth 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," "Fourth Amendment," and "Lenders" and 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 Fourth Amendment to Article or Section
numbers shall be to Articles and Sections of this Fourth Amendment, unless
expressly stated herein to the contrary. References in this Fourth Amendment to
"hereby," "herein," hereinafter," hereinabove," "hereinbelow," "hereof," and
"hereunder" shall be to this Fourth Amendment in its entirety and not only to
the particular Article or Section in which such reference appears.

                                       1
<PAGE>

      1.04 Articles and Sections. This Fourth 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 Fourth 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 Deletion of F-W Oil Exploration L.L.C. F-W Oil Exploration L.L.C. is
hereby deleted from the Agreement and released from all Obligations hereunder.

      2.02 Amendment of Section 2.9(a). Section 2.9(a) of the Agreement shall be
amended to read as follows:

      "2.9 Borrowing Base Determinations. (a) The Borrowing Base as of December
      28, 2004, is acknowledged by the Borrower and the Lenders to be
      $33,880,000."

      2.03 Amendment of Exhibit I. Exhibit I, i.e., the Form of Promissory Note,
shall be as set forth on Exhibit I to this Fourth 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 Agent 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 Fourth Amendment as requested by the
            Agent;

      (b)   the Note;

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

                                       2
<PAGE>

      3.02 Accuracy of Representations and Warranties. The representations and
warranties contained in Article IV of the Agreement and this Fourth 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 Fourth Amendment.

                                   ARTICLE VI
                                  MISCELLANEOUS

      6.01 Scope of Amendment. The scope of this Fourth Amendment is expressly
limited to the matters addressed herein and this Fourth 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 Fourth 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 Fourth Amendment.

      6.03 Parties in Interest. All provisions of this Fourth 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 Fourth 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 FOURTH 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 FOURTH AMENDMENT,
THE AGREEMENT, THE NOTE, THE SECURITY INSTRUMENTS, AND THE OTHER

                                       3
<PAGE>

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 FOURTH 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 FOURTH 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)

                                       4
<PAGE>

      IN WITNESS WHEREOF, this Fourth 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

                                       5
<PAGE>

                                     AGENT AND LENDER

                                     GUARANTY BANK, FSB

                                     By: /s/  Arthur R. Gralla
                                         ---------------------------------------
                                         Arthur R. Gralla, Jr.
                                         Managing Director

                                       6
<PAGE>

                                 PROMISSORY NOTE

$50,000,000                      Houston, Texas                December 28, 2004

      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.

                             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

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