<PAGE>

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


                          CHESAPEAKE ENERGY CORPORATION

                                       and

                     the Subsidiary Guarantors named herein

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

                          8.375% SENIOR NOTES DUE 2008

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


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


                          FOURTH SUPPLEMENTAL INDENTURE


                          DATED AS OF February 14, 2003


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




                              THE BANK OF NEW YORK

                                   as Trustee

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



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


<PAGE>

     THIS FOURTH SUPPLEMENTAL INDENTURE, dated as of February 14, 2003, is among
Chesapeake Energy Corporation, an Oklahoma corporation (the "Company"), each of
the parties identified under the caption "Subsidiary Guarantors" on the
signature page hereto (the "Subsidiary Guarantors") and The Bank of New York, as
Trustee.

                                    RECITALS

     WHEREAS, the Company, the Subsidiary Guarantors a party thereto and the
Trustee entered into an Indenture, dated as of November 5, 2001, as supplemented
prior to the date hereof (the "Indenture"), pursuant to which the Company has
originally issued $250,000,000 in principal amount of 8.375% Senior Notes due
2008 (the "Notes"); and

     WHEREAS, Section 9.01(3) of the Indenture provides that the Company, the
Subsidiary Guarantors and the Trustee may amend or supplement the Indenture
without notice to or consent of any Holder to reflect the addition of any
Subsidiary Guarantor, as provided for in the Indenture; and

     WHEREAS, the Board of Directors of the Company has designated Chesapeake
ORC, L.L.C. as a Restricted Subsidiary of the Company and desires to add such
entity as a Subsidiary Guarantor under the Indenture; and

     WHEREAS, all acts and things prescribed by the Indenture, by law and by the
charter and the bylaws (or comparable constituent documents) of the Company, of
the Subsidiary Guarantors and of the Trustee necessary to make this Fourth
Supplemental Indenture a valid instrument legally binding on the Company, the
Subsidiary Guarantors and the Trustee, in accordance with its terms, have been
duly done and performed;

     NOW, THEREFORE, to comply with the provisions of the Indenture and in
consideration of the above premises, the Company, the Subsidiary Guarantors and
the Trustee covenant and agree for the equal and proportionate benefit of the
respective Holders of the Notes as follows:

                                    ARTICLE 1

     Section 1.01. This Fourth Supplemental Indenture is supplemental to the
Indenture and does and shall be deemed to form a part of, and shall be construed
in connection with and as part of, the Indenture for any and all purposes.

     Section 1.02. This Fourth Supplemental Indenture shall become effective
immediately upon its execution and delivery by each of the Company, the
Subsidiary Guarantors and the Trustee.




                                       2

<PAGE>

                                    ARTICLE 2

     From this date, in accordance with Section 10.03 and by executing this
Fourth Supplemental Indenture, Chesapeake ORC, L.L.C., an Oklahoma limited
liability company, is subject to the provisions of the Indenture as a Subsidiary
Guarantor to the extent provided for in Article Ten thereunder.

                                    ARTICLE 3

     Section 3.01. Except as specifically modified herein, the Indenture and the
Notes are in all respects ratified and confirmed (mutatis mutandis) and shall
remain in full force and effect in accordance with their terms with all
capitalized terms used herein without definition having the same respective
meanings ascribed to them as in the Indenture.

     Section 3.02. Except as otherwise expressly provided herein, no duties,
responsibilities or liabilities are assumed, or shall be construed to be
assumed, by the Trustee by reason of this Fourth Supplemental Indenture. This
Fourth Supplemental Indenture is executed and accepted by the Trustee subject to
all the terms and conditions set forth in the Indenture with the same force and
effect as if those terms and conditions were repeated at length herein and made
applicable to the Trustee with respect hereto.

     Section 3.03. The Company hereby notifies the Trustee that Chesapeake ORC,
L.L.C. has been designated by the Board of Directors of the Company as a
Restricted Subsidiary (as that term is defined in the Indenture).

     Section 3.04. THE LAW OF THE STATE OF NEW YORK SHALL GOVERN AND BE USED TO
CONSTRUE AND ENFORCE THIS FOURTH SUPPLEMENTAL INDENTURE.

     Section 3.05. The parties may sign any number of copies of this Fourth
Supplemental Indenture. Each signed copy shall be an original, but all of such
executed copies together shall represent the same agreement.

                          [NEXT PAGE IS SIGNATURE PAGE]




                                       3

<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Fourth Supplemental
Indenture to be duly executed, all as of the date first written above.

                                 COMPANY:

                                 CHESAPEAKE ENERGY CORPORATION

                                 By /s/ Aubrey K. McClendon
                                   --------------------------------------------
                                 Name: Aubrey K. McClendon
                                       ----------------------------------------
                                 Title: Chief Executive Officer
                                        ---------------------------------------


                                 SUBSIDIARY GUARANTORS:

                                 CHESAPEAKE BETA CORP.
                                 CHESAPEAKE DELTA CORP.
                                 CHESAPEAKE ENERGY LOUISIANA
                                 CORPORATION
                                 CHESAPEAKE OPERATING, INC.
                                 NOMAC DRILLING CORPORATION
                                 CARMEN ACQUISITION, L.L.C.
                                 CHESAPEAKE ACQUISITION, L.L.C.
                                 CHESAPEAKE ENO ACQUISITION, L.L.C.
                                 CHESAPEAKE FOCUS, L.L.C.
                                 CHESAPEAKE KNAN ACQUISITION, L.L.C.
                                 CHESAPEAKE MOUNTAIN FRONT, L.L.C.
                                 CHESAPEAKE ORC, L.L.C.
                                 CHESAPEAKE ROYALTY, L.L.C.
                                 GOTHIC ENERGY, L.L.C.
                                 GOTHIC PRODUCTION, L.L.C.
                                 SAP ACQUISITION, L.L.C.
                                 THE AMES COMPANY, L.L.C.


                                 By /s/ Aubrey K. McClendon
                                   --------------------------------------------
                                 Name: Aubrey K. McClendon
                                       ----------------------------------------
                                 Title: Chief Executive Officer
                                        ---------------------------------------


                                       4

<PAGE>

                                 CHESAPEAKE EXPLORATION LIMITED
                                 PARTNERSHIP
                                 CHESAPEAKE LOUISIANA, L.P.
                                 CHESAPEAKE PANHANDLE LIMITED
                                 PARTNERSHIP
                                 CHESAPEAKE-STAGHORN ACQUISITION L.P.
                                 CHESAPEAKE SIGMA, L.P.

                                 By:  Chesapeake Operating, Inc. as general
                                      partner of each  representative entity

                                 By /s/ Aubrey K. McClendon
                                   --------------------------------------------
                                 Name: Aubrey K. McClendon
                                       ----------------------------------------
                                 Title: Chief Executive Officer
                                        ---------------------------------------


                                 TRUSTEE:

                                 THE BANK OF NEW YORK, as Trustee

                                 By /s/ Louis P. Young
                                   --------------------------------------------
                                 Name: Louis P. Young
                                       ----------------------------------------
                                 Title: Vice President
                                       ----------------------------------------

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