<PAGE>
                                                                   EXHIBIT 4.2.1

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

                          CHESAPEAKE ENERGY CORPORATION

                                       and

                     the Subsidiary Guarantors named herein

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

                          8 1/2% SENIOR NOTES DUE 2012

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


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


                          NINTH SUPPLEMENTAL INDENTURE

                          DATED AS OF December 17, 2001


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


                              THE BANK OF NEW YORK

                             as successor Trustee to

                     United States Trust Company of New York


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


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

<PAGE>

         THIS NINTH SUPPLEMENTAL INDENTURE, dated as of December 17, 2001, 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
successor to United States Trust Company 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 March 15, 1997, as supplemented
prior to the date hereof (the "Indenture"), pursuant to which the Company has
originally issued $150,000,000 in principal amount of 8 1/2% Senior Notes due
2012 (the "Notes"); and

         WHEREAS, Section 9.1(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 or release of
any Subsidiary Guarantor, as provided for in the Indenture; and

         WHEREAS, the Board of Directors of the Company has designated Carmen
Acquisition Corp. and Sap Acquisition Corp. as Restricted Subsidiaries of the
Company and to add such entities as Subsidiary Guarantors 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 Ninth
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 Ninth 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 Ninth Supplemental Indenture shall become effective
immediately upon its execution and delivery by each of the Company, the
Subsidiary Guarantors and the Trustee.

                                    ARTICLE 2

         From this date, in accordance with Section 10.3 and by executing this
Ninth Supplemental Indenture, Carmen Acquisition Corp., an Oklahoma corporation,
is subject to the provisions of the Indenture as a Subsidiary Guarantor to the
extent provided for in Article X thereunder.



NINTH SUPPLEMENTAL INDENTURE (8 1/2%)

                                      -2-
<PAGE>

                                    ARTICLE 3

         Section 3.01. As a result of the merger of Arkoma Pittsburg Holding
Corporation, an Oklahoma corporation ("APHC"), with and into Chesapeake
Exploration Limited Partnership, an Oklahoma limited partnership ("CELP"), which
constitutes a merger with a Subsidiary Guarantor under Section 10.2(a) of the
Indenture, APHC shall for all purposes be released as a Subsidiary Guarantor
from all of its Guarantee and related obligations in the Indenture, pursuant to
Section 10.4(b) of the Indenture. The notation on the Securities relating to the
Guarantee shall be deemed to exclude the name of APHC and the signature of an
Officer of APHC on its behalf.

         Section 3.02. As the surviving entity in its merger with APHC and as a
Subsidiary Guarantor, CELP hereby agrees to assume all of the obligations of
APHC.

                                    ARTICLE 4

         Section 4.01. 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 4.02. 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 Ninth Supplemental Indenture. This
Ninth 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 4.03. The Company hereby notifies the Trustee that Carmen
Acquisition Corp. and Sap Acquisition Corp have each been designated by the
Board of Directors of the Company as a Restricted Subsidiary (as that term is
defined in the Indenture).

         Section 4.04. THE LAW OF THE STATE OF NEW YORK SHALL GOVERN AND BE USED
TO CONSTRUE AND ENFORCE THIS NINTH SUPPLEMENTAL INDENTURE.

         Section 4.05. The parties may sign any number of copies of this Ninth
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]



NINTH SUPPLEMENTAL INDENTURE (8 1/2%)

                                      -3-
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Ninth
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:

                                   CARMEN ACQUISITION CORP.
                                   CHESAPEAKE ACQUISITION CORPORATION
                                   CHESAPEAKE ENERGY LOUISIANA
                                   CORPORATION
                                   CHESAPEAKE MOUNTAIN FRONT CORP.
                                   CHESAPEAKE OPERATING, INC.
                                   CHESAPEAKE ROYALTY COMPANY
                                   GOTHIC ENERGY CORPORATION
                                   GOTHIC PRODUCTION CORPORATION
                                   NOMAC DRILLING CORPORATION
                                   SAP ACQUISITION CORP.
                                   THE AMES COMPANY, INC.


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



NINTH SUPPLEMENTAL INDENTURE (8 1/2%)

                                      -4-
<PAGE>

                                   CHESAPEAKE EXPLORATION LIMITED
                                   PARTNERSHIP
                                   CHESAPEAKE LOUISIANA, L.P.
                                   CHESAPEAKE PANHANDLE LIMITED
                                   PARTNERSHIP
                                   CHESAPEAKE-STAGHORN ACQUISITION 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 successor to United
                                   States Trust Company of New York, as Trustee


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



NINTH SUPPLEMENTAL INDENTURE (8 1/2%)

                                      -5-