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                                                                   EXHIBIT 4.2.1


                        FOURTH SUPPLEMENTAL INDENTURE TO
               INDENTURE DATED MARCH 15, 1997 (8 1/2% SECURITIES)


         FOURTH SUPPLEMENTAL INDENTURE dated as of July 1, 1998, among
CHESAPEAKE ENERGY CORPORATION, an Oklahoma corporation (the "Company"), the
SUBSIDIARY GUARANTORS listed as signatories hereto, UNITED STATES TRUST COMPANY
OF NEW YORK, a New York corporation, as Trustee to the Indenture (as such term
is defined in Article I below) and CHESAPEAKE PANHANDLE LIMITED PARTNERSHIP, an
Oklahoma limited partnership ("CPLP"), CHESAPEAKE ACQUISITIONS, LTD., an
Alberta, Canada corporation ("CAL") and THE AMES COMPANY, INC., an Oklahoma
corporation ("TAC").

         WHEREAS, the Company, the Subsidiary Guarantors and the Trustee have
heretofore entered into the Original Indenture, pursuant to the provisions of
which the Company has heretofore issued $150,000,000 in aggregate principal
amount of the Securities;

         WHEREAS, CPLP, CAL and TAC are Restricted Subsidiaries of the Company
and the parties desire to add CPLP, CAL and TAC as Subsidiary Guarantors under
the Indenture;

         WHEREAS, Chesapeake Merger Corp., an Oklahoma corporation ("CMC"),
Hugoton Energy Corporation, a Kansas corporation ("HEC"), and Hugoton
Exploration Corporation, a Kansas corporation ("HEX"), are Restricted
Subsidiaries of the Company and Subsidiary Guarantors under the Indenture;

         WHEREAS, the parties desire to release CMC, HEC and HEX as Subsidiary
Guarantors under the Indenture because CMC, HEC and HEX have directly or
indirectly merged with and into Chesapeake Mid-Continent Corp., an Oklahoma
corporation ("CMCC"), and CMCC is the surviving entity, a Restricted Subsidiary
of the Company and a Subsidiary Guarantor under the Indenture;

         WHEREAS, HEC Trading Company, a Texas corporation ("HTC"), AmGas
Corporation, a Kansas corporation ("AC"), Tiffany Gathering, Inc., a Texas
corporation ("TGI"), AnSon Gas Marketing, an Oklahoma general partnership
("AGM"), and Mid-Continent Gas Pipeline Company, an Oklahoma general partnership
("MGPC"), are Restricted Subsidiaries of the Company and Subsidiary Guarantors
under the Indenture;

         WHEREAS, the parties desire to release HTC, AC, TGI, AGM and MGPC as
Subsidiary Guarantors under the Indenture because HTC, AC, TGI, AGM and MGPC
have directly or indirectly merged with and into Chesapeake Energy Marketing,
Inc., an Oklahoma corporation ("CEMI"), and CEMI is the surviving entity and an
Unrestricted Subsidiary of the Company and, to the extent required under the
Indenture, each such merger has been treated as an Asset Sale under the
Indenture;



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         WHEREAS, Section 9.1 of the Indenture provides, among other things,
that the Trustee, the Subsidiary Guarantors and the Company 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 by the
Indenture; and

         WHEREAS, the execution and delivery of this Fourth Supplemental
Indenture have been duly authorized by the Company, the Subsidiary Guarantors,
CPLP, CAL and TAC and all actions necessary to make this Fourth Supplemental
Indenture a valid and binding instrument according to its terms and the terms of
the Original Indenture have been performed.

         NOW, THEREFORE, BY THIS FOURTH SUPPLEMENTAL INDENTURE, for and in
consideration of the premises and of the mutual covenants herein contained and
for other valuable considerations, the receipt whereof is hereby acknowledged,
the Company, the Subsidiary Guarantors, CPLP, CAL and TAC covenant and agree
with the Trustee, for the equal benefit of all present and future Holders of the
Securities, as follows:


                                    ARTICLE I

                                   DEFINITIONS

         SECTION 1.1 The definitions set forth in or incorporated by reference
in Article I of the Indenture shall be applicable to this Fourth Supplemental
Indenture, as fully and to the same extent as if set forth herein, except as
otherwise expressly provided herein. As used in this Fourth Supplemental
Indenture, the following terms shall have the following meanings:

         "Indenture" means the Original Indenture, as amended by this Fourth
Supplemental Indenture, relating to the Securities.

         "Original Indenture" means the Indenture dated as of March 15, 1997,
among the Company, the Subsidiary Guarantors listed as signatories thereto and
the Trustee, relating to the Securities, as amended by: (i) that certain First
Supplemental Indenture dated as of December 17, 1997, (ii) that certain Second
Supplemental Indenture dated as of February 16, 1998, and (iii) that certain
Third Supplemental Indenture dated as of April 22, 1998.


                                   ARTICLE II

                        ADDITION OF SUBSIDIARY GUARANTOR

         SECTION 2.1 As a Subsidiary Guarantor, each of CPLP, CAL and TAC
hereby: (a) jointly and severally, unconditionally guarantees to each Holder and
to the Trustee the due and punctual payment of the principal of, premium, if
any, and interest on the Securities and all other amounts due and payable under
the Indenture and the Securities by the Company, whether at maturity, by
acceleration, redemption, repurchase or otherwise including, without


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limitation, interest on the overdue principal of, premium, if any, and interest
on the Securities to the extent lawful, all in accordance with the terms and
subject to the limitations of the Indenture as if each of CPLP, CAL and TAC had
been an original party thereto; and (b) subjects each of CPLP, CAL and TAC to
the provisions (including the representations and warranties) of the Indenture
as a Subsidiary Guarantor.


                                   ARTICLE III

                         RELEASE OF SUBSIDIARY GUARANTOR

         SECTION 3.1 As a result of the direct or indirect merger with CMCC,
which constitutes a merger with a Subsidiary Guarantor under Section 10.2(a) of
the Indenture, CMC, HEC and HEX shall for all purposes be released as a
Subsidiary Guarantor from all of their Guarantee and related obligations in the
Indenture, pursuant to Section 10.4(b) of the Indenture.

         SECTION 3.2 As a result of the direct or indirect merger with CEMI,
which constitutes an Asset Sale under Section 10.2(b) of the Indenture, HTC, AC,
TGI, AGM and MGPC shall for all purposes be released as a Subsidiary Guarantor
from all of their Guarantee and related obligations in the Indenture, pursuant
to Section 10.4(b) of the Indenture.

         SECTION 3.3 The notation on the Securities relating to the Guarantee
shall be deemed to exclude the names of CMC, HEC, HEX, HTC, AC, TGI, AGM and
MGPC and the signature of an Officer on behalf of CMC, HEC, HEX, HTC, AC, TGI,
AGM and MGPC.


                                   ARTICLE IV

                            ASSUMPTION OF OBLIGATIONS

         SECTION 4.1 As the surviving entity in the merger with CMC, HEC and
HEX, and as a Subsidiary Guarantor, CMCC hereby agrees to assume all the
obligations of CMC, HEC and HEX.


                                    ARTICLE V

                                  MISCELLANEOUS

         SECTION 5.1 This Fourth Supplemental Indenture is a supplemental
indenture pursuant to Section 9.1 of the Indenture. Upon execution and delivery
of this Fourth Supplemental Indenture, the terms and conditions of this Fourth
Supplemental Indenture will be part of the terms and conditions of the Indenture
for any and all purposes, and all the terms and


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conditions of both shall be read together as though they constitute one
instrument, except that in case of conflict, the provisions of this Fourth
Supplemental Indenture will control.

         SECTION 5.2 Except as they have been modified in this Fourth
Supplemental Indenture, each and every term and provision of the Indenture shall
remain in full force and effect.

         SECTION 5.3 This Fourth Supplemental Indenture may be executed in any
number of counterparts, each of which when so executed and delivered shall be an
original, but such counterparts shall together constitute but one and the same
instrument.

         SECTION 5.4 This Fourth Supplemental Indenture shall be governed by and
construed in accordance with the laws of the State of New York without giving
effect to applicable principals of conflicts of law to the extent that the
application of the law of another jurisdiction would be required thereby.


                                   SIGNATURES

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



                                    UNITED STATES TRUST COMPANY OF NEW YORK, 
                                    a New York corporation, as Trustee


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

                                    CHESAPEAKE ENERGY CORPORATION, an
                                    Oklahoma corporation


                                    By  /s/ AUBREY K. MCCLENDON
                                      ------------------------------------------
                                       Aubrey K. McClendon, Chief Executive 
                                       Officer






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                                  CHESAPEAKE PANHANDLE LIMITED
                                  PARTNERSHIP, an Oklahoma limited partnership

                                  By   Chesapeake Operating, Inc., an Oklahoma
                                       corporation, Sole General Partner


                                       By /s/ AUBREY K. MCCLENDON
                                         ---------------------------------------
                                          Aubrey K. McClendon,
                                          Chief Executive Officer


                                  CHESAPEAKE ACQUISITIONS, LTD., an
                                  Alberta, Canada corporation


                                  By /s/ AUBREY K. MCCLENDON
                                    --------------------------------------------
                                    Aubrey K. McClendon, Chief Executive Officer

                                  THE AMES COMPANY, INC., an Oklahoma
                                  corporation


                                  By /s/ AUBREY K. MCCLENDON
                                    --------------------------------------------
                                    Aubrey K. McClendon, Chief Executive Officer


                                  SUBSIDIARY GUARANTORS

                                  CHESAPEAKE OPERATING, INC., an Oklahoma
                                  corporation


                                  By /s/ AUBREY K. MCCLENDON
                                    --------------------------------------------
                                    Aubrey K. McClendon, Chief Executive Officer

                                  CHESAPEAKE ENERGY LOUISIANA
                                  CORPORATION, an Oklahoma corporation


                                  By /s/ AUBREY K. MCCLENDON
                                    --------------------------------------------
                                    Aubrey K. McClendon, Chief Executive Officer



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                                  CHESAPEAKE ACQUISITION CORPORATION,
                                  an Oklahoma corporation


                                  By /s/ AUBREY K. MCCLENDON
                                    --------------------------------------------
                                    Aubrey K. McClendon, Chief Executive Officer

                                  CHESAPEAKE MID-CONTINENT CORP., an
                                  Oklahoma corporation


                                  By /s/ AUBREY K. MCCLENDON
                                    --------------------------------------------
                                    Aubrey K. McClendon, Chief Executive Officer


                                  CHESAPEAKE GOTHIC CORP., an Oklahoma
                                  corporation


                                  By /s/ AUBREY K. MCCLENDON
                                    --------------------------------------------
                                    Aubrey K. McClendon, Chief Executive Officer

                                  CHESAPEAKE CANADA CORPORATION, an
                                  Alberta, Canada corporation


                                  By /s/ AUBREY K. MCCLENDON
                                    --------------------------------------------
                                    Aubrey K. McClendon, Chief Executive Officer

                                  CHESAPEAKE EXPLORATION LIMITED
                                  PARTNERSHIP, an Oklahoma limited partnership

                                  By  Chesapeake Operating, Inc., an Oklahoma
                                      corporation, Sole General Partner


                                      By /s/ AUBREY K. MCCLENDON
                                        ----------------------------------------
                                        Aubrey K. McClendon,
                                        Chief Executive Officer




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                                  CHESAPEAKE LOUISIANA, L.P., an Oklahoma
                                  limited partnership

                                  By  Chesapeake Operating, Inc., an
                                      Oklahoma corporation, Sole General Partner


                                      By /s/ AUBREY K. MCCLENDON
                                        ----------------------------------------
                                        Aubrey K. McClendon,
                                        Chief Executive Officer





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