FOURTH AMENDMENT TO AMENDED AND RESTATED CREDIT AGREEMENT

Exhibit 10.22.5.5

FOURTH AMENDMENT TO

AMENDED AND RESTATED CREDIT AGREEMENT

AMONG

PRIMEENERGY CORPORATION

PRIMEENERGY MANAGEMENT CORPORATION

PRIME OPERATING COMPANY

EASTERN OIL WELL SERVICE COMPANY

SOUTHWEST OILFIELD CONSTRUCTION COMPANY

EOWS MIDLAND COMPANY

GUARANTY BANK, FSB

AS AGENT AND LETTER OF CREDIT ISSUER

AND

THE LENDERS SIGNATORY HERETO

Effective

February 8, 2008

REVOLVING LINE OF CREDIT OF UP TO $150,000,000

AND

REVOLVING LINE OF CREDIT OF UP TO $10,000,000

TABLE OF CONTENTS

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FOURTH AMENDMENT TO

AMENDED AND RESTATED CREDIT AGREEMENT

This FOURTH AMENDMENT TO AMENDED AND RESTATED CREDIT AGREEMENT (this “ Amendment ”) is made and entered into effective as of February 8, 2008 (the “ Effective Date ”), by and among 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 ”), each lender that is a signatory hereto (collectively, the “ Lenders ”) and GUARANTY BANK, FSB , a federal savings bank, as agent for the Lenders under the Amended and Restated Credit Agreement, as amended, referred to hereinafter (in such capacity, the “ Agent ”).

WITNESSETH

WHEREAS, the Borrower, the Agent and the Lenders did execute and exchange counterparts of that certain Amended and Restated Credit Agreement dated December 28, 2006, as amended by First Amendment to Amended and Restated Credit Agreement dated effective as of July 17, 2007, Second Amendment to Amended and Restated Credit Agreement dated effective as of October 9, 2007 and Third Amendment to Amended and Restated Credit Agreement dated effective January 22, 2008 (as so amended, the “Agreement”);

WHEREAS, the Borrower, the Agent and the Lenders 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 herein, the parties hereto agree as follows:

ARTICLE I

DEFINITIONS AND INTERPRETATION

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

1.2 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.

1.3 References . References in this Amendment to Schedule, Exhibit, Article, or Section numbers shall be to Schedules, Exhibits, Articles, or Sections of this Amendment, unless expressly stated to the contrary. References in this Amendment to “hereby,” “herein,” “hereinafter,” “hereinabove,” “hereinbelow,” “hereof,” “hereunder” and words of similar import

shall be to this Amendment in its entirety and not only to the particular Schedule, Exhibit, Article, or Section in which such reference appears. Specific enumeration herein shall not exclude the general and, in such regard, the terms “includes” and “including” used herein shall mean “includes, without limitation,” or “including, without limitation,” as the case may be, where appropriate. Except as otherwise indicated, references in this Amendment to statutes, sections, or regulations are to be construed as including all statutory or regulatory provisions consolidating, amending, replacing, succeeding, or supplementing the statute, section, or regulation referred to. References in this Amendment to “writing” include printing, typing, lithography, facsimile reproduction, and other means of reproducing words in a tangible visible form. References in this Amendment to amendments and other contractual instruments shall be deemed to include all exhibits and appendices attached thereto and all subsequent amendments and other modifications to such instruments, but only to the extent such amendments and other modifications are not prohibited by the terms of this Amendment. References in this Amendment to Persons include their respective successors and permitted assigns.

1.4 Articles and Sections . This Amendment, for convenience only, has been divided into Articles and Sections; and it is understood that the rights