Exhibit 4.2 FIRST SUPPLEMENTAL INDENTURE FIRST SUPPLEMENTAL INDENTURE dated as of July 28, 2005 among PETROHAWK ENERGY CORPORATION, a Delaware corporation (the "Company") and the successor by way of merger to Mission Resources Corporation, a Delaware corporation ("Mission"), the parties listed on the signature page hereof as Existing Subsidiary Guarantors (each, an "Existing Subsidiary Guarantor"), the parties listed on the signature page hereof as Additional Subsidiary Guarantors (each, an "Additional Subsidiary Guarantor"), and THE BANK OF NEW YORK TRUST COMPANY, N.A., a national association (the "Trustee"), as successor trustee to The Bank of New York, to the Indenture dated as of April 8, 2004 (the "Indenture", capitalized terms used herein and not otherwise defined having the respective meanings specified in the Indenture) among Mission, the Subsidiary Guarantors named therein and the Trustee. RECITALS A. Mission has merged (the "Merger") with and into the Company on the date hereof, and the Company is the survivor of the Merger. B. The Company is entering into this First Supplemental Indenture pursuant Section 8.1(A)(1)(b) of the Indenture in order expressly to assume all the obligations of Mission under the Notes and the Indenture. C. Each Existing Subsidiary Guarantor is entering into this First Supplemental Indenture pursuant to Section 8.1(A)(6) of the Indenture to confirm that its Subsidiary Guarantee of the Notes will apply to the Company's obligations under the Indenture and the Notes. D. Each Additional Subsidiary Guarantor is entering into this First Supplemental Indenture pursuant to Section 10.12 of the Indenture to evidence its agreement to be an additional Subsidiary Guarantor under the Indenture. E. The entering into of this First Supplemental Indenture without the consent of any Holder is permitted under Sections 9.1(a) and 9.1(g) of the Indenture. NOW, THEREFORE, THIS FIRST SUPPLEMENTAL INDENTURE WITNESSETH: 1. The Company expressly assumes all the obligations of Mission under the Notes and the Indenture. 2 2. Each Existing Subsidiary Guarantor confirms that its Subsidiary Guarantee of the Notes will apply to the Company's obligations under the Indenture and the Notes. 3. Each Additional Subsidiary Guarantor: (a) (i) accepts and assumes all obligations of, and agrees that it is, an additional Subsidiary Guarantor under the Indenture and (ii) unconditionally, jointly and severally, enters into and makes the Subsidiary Guarantee as provided in Article 13 of the Indenture; provided that, as provided in Section 10.12(b) of the Indenture, the obligations of each Additional Subsidiary Guarantor under the Indenture will be automatically and unconditionally released and discharged upon the terms and conditions set forth in Section 13.3 of the Indenture; (b) waives and agrees not to claim or take the benefit or advantage of, in any manner whatsoever, any rights of reimbursement, indemnity or subrogation or any other rights against the Company or any other Restricted Subsidiary as a result of any payment by such Restricted Subsidiary under its Subsidiary Guarantee until such time as the obligations guaranteed thereby are paid in full; and (c) represents that it is a Restricted Subsidiary of the Company under the Indenture. 4. Sections 1, 2 and 3 of this First Supplemental Indenture shall become effective immediately upon the satisfaction of the conditions to the Merger set forth in Section 8.1 of the Indenture and the satisfaction of the requirements of Section 9.3 of the Indenture with respect to this First Supplemental Indenture. 5. Upon the effectiveness of Sections 1, 2 and 3 hereof, on and after the date hereof each reference in the Indenture to "this Indenture", "hereunder", "hereof" or words of like import referring to the Indenture, and each reference in the Notes or the Subsidiary Guarantees to the "Indenture", "thereunder", "thereof" or words of like import referring to the Indenture, shall mean and be a reference to the Indenture as supplemented hereby and each reference in the Notes to "this Note", "hereunder", "hereof" or words of like import referring to the Notes shall mean and be a reference to the Notes as supplemented hereby and each reference in the Subsidiary Guarantees to "the Notes", "thereunder", "thereof" or words of like import referring to the Notes shall mean and be a reference to the Notes as supplemented hereby. Each reference in the Indenture, the Notes, or related documents to Subsidiary Guarantor shall mean and be a reference to the Existing Subsidiary Guarantors and to the Additional Subsidiary Guarantors. 3 6. Except as specifically supplemented above, the Indenture, the Notes and the Subsidiary Guarantees are and shall continue to be in full force and effect and are hereby in all respects ratified and confirmed. 7. This First Supplemental Indenture may be executed in any number of counterparts and by different parties hereto in separate counterparts, each of which when so executed and delivered shall be deemed to be an original and all of which taken together shall constitute but one and the same agreement. Deliver of an executed signature page hereof by facsimile transmission shall be effective as delivery of an original executed signature page hereof. 8. This First Supplemental Indenture shall be governed by, and construed in accordance with, the law of the State of New York. 4 IN WITNESS WHEREOF, the parties hereto have caused this First Supplemental Indenture to be executed by their respective officers thereunto duly authorized, as of the date first-above written. PETROHAWK ENERGY CORPORATION THE BANK OF NEW YORK TRUST COMPANY, N.A., as successor trustee to The Bank of New York By By ------------------------------------- ---------------------------------- Floyd C. Wilson Patrick T. Giordano President and Chief Executive Officer Vice President EXISTING SUBSIDIARY GUARANTORS: BLACK HAWK OIL COMPANY MISSION E&P LIMITED PARTNERSHIP By: BLACK HAWK OIL COMPANY Its General Partner By By ------------------------------------- ---------------------------------- Floyd C. Wilson Floyd C. Wilson President and Chief Executive Officer President and Chief Executive Officer MISSION HOLDINGS LLC By ------------------------------------- Connie D. Tatum President ADDITIONAL SUBSIDIARY GUARANTORS: BETA OPERATING COMPANY, L.L.C. P-H ENERGY, LLC By: PETROHAWK ENERGY CORPORATION Its Sole Member By By ------------------------------------- ---------------------------------- Floyd C. Wilson Floyd C. Wilson President and Chief Executive Officer President and Chief Executive Officer PROHAWK OIL & GAS CORPORATION PETROHAWK OPERATING COMPANY By By ------------------------------------- ---------------------------------- Floyd C. Wilson Floyd C. Wilson President and Chief Executive Officer President and Chief Executive Officer RED RIVER FIELD SERVICES, L.L.C. TCM, L.L.C. By: BETA OPERATING COMPANY, L.L.C. By: BETA OPERATING COMPANY, L.L.C. Its Sole Member Its Sole Member By: PETROHAWK ENERGY CORPORATION By: PETROHAWK ENERGY CORPORATION Its Sole Member Its Sole Member By By ------------------------------------- ---------------------------------- Floyd C. Wilson Floyd C. Wilson President and Chief Executive Officer President and Chief Executive Officer PETROHAWK PROPERTIES, LP PROHAWK OPERATING, LLC By: P-H Energy, LLC By: PROHAWK OIL & GAS CORPORATION Its General Partner Its Sole Member-Manager By By ------------------------------------- ---------------------------------- Floyd C. Wilson Floyd C. Wilson President and Chief Executive Officer President and Chief Executive Officer PETROHAWK HOLDINGS, LLC By ------------------------------------- Connie D. Tatum President