Exhibit 10.42

ASSUMPTION AGREEMENT

ASSUMPTION AGREEMENT, dated as of January 20, 2009, made by KCS Resources, LLC,
a limited liability company duly formed and existing under the laws of the state
of Delaware (the “Additional Grantor”), in favor of BNP Paribas, as
administrative agent (in such capacity, the “Administrative Agent”) for the
banks and other financial institutions (the “Lenders”) parties to the Credit
Agreement referred to below. All capitalized terms not defined herein shall have
the meaning ascribed to them in such Credit Agreement.

W I T N E S S E T H:

WHEREAS, Petrohawk Energy Corporation (the “Borrower”), the Lenders, the
Administrative Agent and the other Agents, have entered into the Third Amended
and Restated Senior Revolving Credit Agreement, dated as of September 10, 2008
(as amended, supplemented or otherwise modified from time to time, the “Credit
Agreement”);

WHEREAS, in connection with the Credit Agreement, the Borrower and certain of
its Subsidiaries have entered into the Third Amended and Restated Guarantee and
Collateral Agreement, dated as of September 10, 2008 (as amended, supplemented
or otherwise modified from time to time, the “Guarantee and Collateral
Agreement”) in favor of the Administrative Agent for the benefit of the Lenders
and Affiliates of the Lenders;

WHEREAS, the Credit Agreement requires the Additional Grantor to become a party
to the Guarantee and Collateral Agreement; and

WHEREAS, the Additional Grantor has agreed to execute and deliver this
Assumption Agreement in order to become a party to the Guarantee and Collateral
Agreement;

NOW, THEREFORE, IT IS AGREED:

1. Guarantee and Collateral Agreement. By executing and delivering this
Assumption Agreement, the Additional Grantor, as provided in Section 10.13 of
the Guarantee and Collateral Agreement, hereby becomes a party to the Guarantee
and Collateral Agreement as a Grantor thereunder with the same force and effect
as if originally named therein as a Grantor and, without limiting the generality
of the foregoing, hereby expressly assumes all obligations and liabilities of a
Grantor thereunder and expressly grants to the Administrative Agent, for the
benefit of the Secured Parties (as defined in the Guarantee and Collateral
Agreement), a security interest in all Collateral owned by such Additional
Grantor to secure all of such Additional Grantor’s obligations and liabilities
thereunder. The information set forth in Annex 1-A hereto is hereby added to the
information set forth in Schedules 1 through 5 to the Guarantee and Collateral
Agreement. The Additional Grantor hereby represents and warrants that each of
the representations and warranties contained in Article IV of the Guarantee and
Collateral Agreement is true and correct on and as of the date hereof (after
giving effect to this Assumption Agreement) as if made on and as of such date.

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2. Governing Law. THIS ASSUMPTION AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED
AND INTERPRETED IN ACCORDANCE WITH, THE LAW OF THE STATE OF TEXAS.

IN WITNESS WHEREOF, the undersigned has caused this Assumption Agreement to be
duly executed and delivered as of the date first above written.

 

KCS RESOURCES, LLC By:  

/s/ Floyd C. Wilson

Name:   Floyd C. Wilson Title:   President and Chief Executive Officer

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ANNEX 1-A

Schedule 1

NOTICE ADDRESSES OF GRANTORS

 

1. KCS Resources, LLC

Delaware limited liability company

Notice Address:

Attn: Floyd C. Wilson

1000 Louisiana, Suite 5600

Houston, Texas 77002

Telephone: (832) 204-2700

Facsimile: (832) 204-2800

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Schedule 2

DESCRIPTION OF PLEDGED SECURITIES

 

Owner

  

Issuer

  

Class of Stock or

other Equity Interest

   No. of
Shares    Certificate No.

KCS Resources, LLC

   Medallion California Properties Company    Common Stock    1000    3

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Schedule 3

FILINGS AND OTHER ACTIONS

REQUIRED TO PERFECT SECURITY INTERESTS

Uniform Commercial Code Filings

1. Financing Statements in respect of the Third Amended and Restated Guaranty
and Collateral Agreement dated as of September 10, 2008 by the Borrower, the
Restricted Subsidiaries party thereto as Guarantors, in favor of the
Administrative Agent and the Lenders for the following entities:

 

  (a) KCS Resources, LLC (Delaware)

2. Stock Powers for the following entity:

 

  (a) Medallion California Properties Company

3. Delivery to Administrative Agent of Pledged Securities:

 

  (a) Medallion California Properties Company

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Schedule 4

CORRECT LEGAL NAME, LOCATION OF JURISDICTION OF ORGANIZATION,

ORGANIZATIONAL IDENTIFICATION NUMBER, TAXPAYOR IDENTIFICATION

NUMBER AND CHIEF EXECUTIVE OFFICE

 

1.   KCS Resources, LLC         a Delaware limited liability company        
Notice Address:         Organizational Identification Number:    2353570     
Federal Identification Number:    86-0876964      Chief Executive Office:   
1000 Louisiana, Suite 5600         Houston, Texas 77002   

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Schedule 5

PRIOR NAMES AND PRIOR CHIEF EXECUTIVE OFFICE

 

3.   KCS Resources, LLC         Prior Names:    KCS Resources, Inc.      Prior
Chief Executive Office:    1000 Louisiana, Suite 5600         Houston, Texas
77002         5555 San Felipe, Suite 1200         Houston, Texas 77056