Document:

<PAGE>
                                                                     EXHIBIT 4.1

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                             PARKER DRILLING COMPANY
                            and Subsidiary Guarantors

                          9 3/4% SENIOR NOTES DUE 2006

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

                          THIRD SUPPLEMENTAL INDENTURE

                           Dated as of April 30, 2002

             Supplementing the Indenture dated as of March 11, 1998

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

                              JPMORGAN CHASE BANK,
                                   as Trustee

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<PAGE>

                          THIRD SUPPLEMENTAL INDENTURE

         This Third Supplemental Indenture dated and effective as of April 30,
2002 (the "Third Supplemental Indenture") is made and entered into by and among
Parker Drilling Company, a Delaware corporation (the "Company"), each of the
parties identified under the caption "Existing Subsidiary Guarantors" on the
signature pages hereof (the "Existing Subsidiary Guarantors"), each of the
parties identified under the caption "New Subsidiary Guarantors" on the
signature pages hereof (the "New Guarantors") and JPMorgan Chase Bank, a New
York banking organization, as Trustee (the "Trustee"), formerly known as The
Chase Manhattan Bank and successor by merger to Chase Bank of Texas, National
Association.

                RECITALS OF THE COMPANY AND SUBSIDIARY GUARANTORS

         WHEREAS, the Company, the Existing Subsidiary Guarantors and the
Trustee have executed and delivered an Indenture dated as of March 11, 1998 by
and among the Company, the Trustee and the Subsidiary Guarantors (as
supplemented by the First and Second Supplemental Indentures, the "1998
Indenture") for the benefit of one another and for the ratable benefit of the
Holders of the 9 3/4% Senior Notes due 2006, Series D (the "Notes") and pursuant
to which the Existing Subsidiary Guarantors have agreed, jointly and severally,
to unconditionally guarantee the due and punctual payment of the principal of,
premium, if any, and interest on the Notes and all other amounts due and payable
under the 1998 Indenture and the Notes by the Company ; and

         WHEREAS, Section 9.01(a)(vi) and (vi) of the 1998 Indenture provides
that under certain conditions the Company and the Trustee may, without the
consent of any Holder of a Note, amend or supplement the 1998 Indenture to add
any Restricted Subsidiary as an additional Subsidiary Guarantor as provided in
Section 10.02 of the 1998 Indenture or to evidence the succession of another
Person to any Existing Subsidiary Guarantor pursuant to Section 10.04 of the
1998 Indenture and the assumption by any such additional Subsidiary Guarantor of
the covenants and agreements of such Subsidiary Guarantor contained in the 1998
Indenture and in the Subsidiary Guarantee of such Subsidiary Guarantor and to
release a Subsidiary Guarantor pursuant to Section 10.05;

         WHEREAS, the Company has determined that the New Guarantors are
required to be added as Subsidiary Guarantors pursuant to Section 10.02 of the
1998 Indenture as a result of said New Guarantors having guaranteed the
Indebtedness of the Company under the Senior Credit Facility;

         WHEREAS, Section 10.02 of the 1998 Indenture provides that as a result
of said actions the following is required: (i) the execution and delivery by the
New Guarantors of this Third Supplemental Indenture whereby the New Guarantors
agree to be bound by the terms of the 1998 Indenture as applicable to a
Subsidiary Guarantor; and (ii) the execution of a Subsidiary Guarantee of the
Notes by the New Guarantors; and

         WHEREAS, the Company has determined that certain Subsidiary Guarantors
should be released from their obligations under the Indenture and its respective
Subsidiary Guarantee as a result of being merged into an Existing Subsidiary
Guarantor; and

         WHEREAS, the execution and delivery of this Third Supplemental
Indenture has been duly authorized by a Board Resolution of the respective
Boards of the Company, the Existing Subsidiary Guarantors and each of the New
Guarantors; and

         WHEREAS, all conditions and requirements necessary to make this Third
Supplemental Indenture valid and binding upon the Company, the Existing
Subsidiary Guarantors and the New

                                      -1-
<PAGE>

Guarantors, and enforceable against the Company, the Existing Subsidiary
Guarantors and the New Guarantors in accordance with its terms, have been
performed and fulfilled.

         NOW, THEREFORE, in consideration of the above premises, the parties
hereto mutually covenant and agree for the equal and ratable benefit of the
respective Holders of the Notes, as follows:

                                    ARTICLE I

                                 NEW GUARANTORS

         Section 1.1. New Guarantors. The New Guarantors, by execution and
delivery of this Third Supplemental Indenture, hereby agree to be bound by the
terms of the Indenture as a Subsidiary Guarantor.

         Section 1.2. Guarantee of Each New Guarantor. Attached as Exhibit A and
incorporated herein by reference is the Subsidiary Guarantee of each New
Guarantor in the form prescribed in the 1998 Indenture, by which each New
Guarantor agrees to guarantee the obligations of the Company, in accordance with
the terms set out in the Subsidiary Guarantee.

                                   ARTICLE II

                              RELEASE OF GUARANTORS

         Section 2.1 Merger of Guarantors. On or about July 31, 1998, Hercules
Rig Corp. merged into Hercules Offshore Corporation and Parker Drilling Offshore
Company merged into Hercules Offshore Corporation in accordance with Section
10.04.

         Section 2.2 Release of Guarantors. Because Hercules Offshore
Corporation, now Parker Drilling Offshore Corporation, is an Existing Guarantor,
and has executed a supplemental indenture to the Indenture and a Subsidiary
Guarantee, Hercules Rig Corp. and Parker Drilling Offshore Company are hereby
released from any further obligations under the Indenture and their respective
Subsidiary Guarantees in accordance with Section 10.05.

                                   ARTICLE III

                    PARTICULAR REPRESENTATIONS AND COVENANTS

         Section 3.1. Authority. The Company and each Existing Subsidiary
Guarantor is duly authorized by a resolution of its respective Board of
Directors to execute and deliver this Third Supplemental Indenture, and all
corporate action on its part required for the execution and delivery of this
Third Supplemental Indenture has been duly and effectively taken.

         Section 3.2. Correctness of Recitals. The Company and each Existing
Subsidiary Guarantor represent and warrant that all recitals and statements in
this Third Supplemental Indenture are true and correct.

                                   ARTICLE IV

                             CONCERNING THE TRUSTEE

         Section 4.1 Acceptance of Trusts. The Trustee accepts the trusts
hereunder and agrees to perform same, but only upon the terms and conditions set
forth in the Indenture.

                                      -2-
<PAGE>

         Section 4.2 Responsibility for Recitals. The recitals and statements
contained in this Third Supplemental Indenture shall be taken as recitals and
statements of the Company, the Existing Subsidiary Guarantors and the Trustee
assumes no responsibility for the correctness of same. The Trustee makes no
representations as to the validity or sufficiency of this Third Supplemental
Indenture, except that the Trustee is duly authorized to deliver it.

                                    ARTICLE V

                            MISCELLANEOUS PROVISIONS

         Section 5.1 Relation to the 1998 Indenture. This Third Supplemental
Indenture shall become effective immediately upon execution and delivery. All
terms and conditions in it shall form a part of the 1998 Indenture as fully and
with the same effect as if all such terms and conditions had been set forth in
the 1998 Indenture. The 1998 Indenture is hereby ratified and confirmed and
shall remain and continue in full force and effect in accordance with its terms,
as supplemented by this Third Supplemental Indenture. The 1998 Indenture and the
Third Supplemental Indenture shall be read, taken and construed together as one
instrument. Capitalized terms used but not defined in this Third Supplemental
Indenture have the meaning ascribed to such terms in the 1998 Indenture.

         Section 5.2 Execution in Counterparts. This Third Supplemental
Indenture may be executed in several counterparts, each of which shall be deemed
an original, but all of which together shall constitute one instrument.

         Section 5.3 Governing Law. The internal laws of the State of New York
shall govern and be used to construe this Third Supplemental Indenture and the
new notations of Subsidiary Guarantees executed and delivered pursuant to it.

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

                                        PARKER DRILLING COMPANY

                                        By:     /s/ James J. Davis
                                           ------------------------------------
                                        Name:   James J. Davis
                                        Title:  Sr. Vice President-Finance and
                                                Chief Financial Officer

                                        JPMORGAN CHASE BANK, as Trustee

                                        By:    /s/ Mauri J. Cowen
                                           ------------------------------------
                                        Name:  Mauri J. Cowen
                                        Title: Vice President and Trust Officer

                                      -3-
<PAGE>

                            EXISTING SUBSIDIARY GUARANTORS:

                            Parker Drilling Company of Oklahoma, Incorporated
                            Parker Drilling Company Limited (Nevada)
                            Parker Drilling Company Limited (Oklahoma)
                            Choctaw International Rig Corp.
                            Parker Drilling Company of New Guinea, Inc.
                            Parker Drilling Company North America, Inc.
                            Parker-VSE, Inc.  (formerly Vance Systems
                               Engineering, Inc.)
                            DGH, Inc.
                            Parker Drilling Company International Limited
                            Parker USA Drilling Company (formerly Parcan
                               Limited)
                            Parker Technology, L.L.C.
                            Parker Technology, Inc.
                            Parker Drilling U.S.A. Ltd.
                            Parker Drilling Offshore Corporation (formerly
                               Hercules Offshore Corporation)
                            Parker Drilling Offshore International, Inc.

                            By:    /s/ David W. Tucker
                               ------------------------------------------------
                            Name:  David W. Tucker
                            Its:   Vice President & Treasurer

                            Quail Tools, L.L.P.

                            By:    /s/ James J. Davis
                               ------------------------------------------------
                            Name:  James J. Davis
                            Its:   Vice President & Treasurer

                            Parker Drilling Offshore USA, L.L.C. (formerly
                               Mallard Bay Drilling, L.L.C.)

                            By:    /s/ Bruce J. Korver
                               ------------------------------------------------
                            Name:  Bruce J. Korver
                            Its:   Vice President-Finance

                            NEW GUARANTORS:

                            Anachoreta, Inc.
                            Pardril, Inc.
                            Parker Aviation, Inc.
                            Parker Drilling (Kazakhstan), Ltd.
                            Parker Drilling Company of Niger
                            Parker North America Operations, Inc.
                            Selective Drilling Corporation
                            Universal Rig Service Corp.

                                       -4-
<PAGE>

                            By: /s/ David W. Tucker
                               ------------------------------------------
                            Name:  David W. Tucker
                            Its:   Vice President & Treasurer

                            Parker Drilling Management Services, Inc.
                            Creek International Rig Corp.

                            By: /s/ Bruce J. Korver
                               ------------------------------------------
                            Name:  Bruce J. Korver
                            Its:   Vice President & Treasurer

                                      -5-<PAGE>
                                                                     EXHIBIT 4.2

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                             PARKER DRILLING COMPANY
                            and Subsidiary Guarantors

                          9 3/4% SENIOR NOTES DUE 2006

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

                          FOURTH SUPPLEMENTAL INDENTURE

                             Dated as of May 2, 2002

             Supplementing the Indenture dated as of March 11, 1998

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

                              JPMORGAN CHASE BANK,
                                   as Trustee

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<PAGE>

                          FOURTH SUPPLEMENTAL INDENTURE

         This Fourth Supplemental Indenture dated and effective as of May 2,
2002 (the "Fourth Supplemental Indenture") is made and entered into by and among
Parker Drilling Company, a Delaware corporation (the "Company"), each of the
parties identified under the caption "Subsidiary Guarantors" on the signature
pages hereof (the "Subsidiary Guarantors") and JPMorgan Chase Bank, a New York
banking organization, as Trustee (the "Trustee"), formerly known as The Chase
Manhattan Bank and successor by merger to Chase Bank of Texas, National
Association.

                                    RECITALS:

         WHEREAS, the Company, the Subsidiary Guarantors and the Trustee have
executed and delivered an Indenture dated as of March 11, 1998 by and among the
Company, the Trustee and the Subsidiary Guarantors (as supplemented by the
First, Second and Third Supplemental Indentures, the "1998 Indenture") for the
benefit of one another and for the ratable benefit of the Holders of the 9 3/4%
Senior Notes due 2006, Series D (the "Notes") and pursuant to which the
Subsidiary Guarantors have agreed, jointly and severally, to unconditionally
guarantee the due and punctual payment of the principal of, premium, if any, and
interest on the Notes and all other amounts due and payable under the 1998
Indenture and the Notes by the Company; and

         WHEREAS, the Company has made an exchange offer pursuant to which the
Company has agreed to exchange up to $250,000,000 of the outstanding Notes for
an equal principal amount of its 10 1/8 % Senior Notes due 2009 ("New Notes") as
more fully described in the Company's Confidential Offering Circular dated April
1, 2002 (the "Exchange Offer"); and

         WHEREAS, in accordance with Section 9.02 of the 1998 Indenture, the
Trustee, the Company and the Subsidiary Guarantors may waive, amend or
supplement provisions of the 1998 Indenture with the consent of the Holders of
at least a majority in aggregate principal amount of the Notes then outstanding,
including consents obtained in connection with a purchase of, or tender offer or
exchange offer for, the Notes; and

         WHEREAS, concurrently with and as a condition to the Holders
participating in the Exchange Offer, the Company has solicited consents from the
Holders to the amendments contained in this Fourth Supplemental Indenture, and
the Company has received consents thereto from Holders of at least a majority in
principal amount of the Notes outstanding as of the date hereof; and

         WHEREAS, all conditions and requirements necessary to make this Fourth
Supplemental Indenture valid and binding upon the Company and the Subsidiary
Guarantors, and enforceable against the Company and the Subsidiary Guarantors in
accordance with its terms, have been performed and fulfilled;

         NOW, THEREFORE, in consideration of the above premises, the parties
hereto mutually covenant and agree for the equal and ratable benefit of the
respective Holders of the Notes, as follows:

         SECTION 1. Certain Terms Defined in the 1998 Indenture. All capitalized
terms used and not otherwise defined herein shall have the meanings ascribed to
them in the 1998 Indenture.

                                      -1-
<PAGE>

         SECTION 2. Amendment of Certain Definitions. The following definitions
in Section 1.01 of the 1998 Indenture shall be amended as follows:

                  (a)      Amend the definition of Net Income by deleting clause
                           (iii) and inserting the word "and" immediately before
                           clause (ii);

                  (b)      Amend the definition of Permitted Investments by
                           changing the reference to $12 million in clause (vii)
                           to $35 million; and

                  (c)      Amend the definition of Permitted Investments by
                           adding the following clause (viii) to the end of the
                           definition: "; and (viii) Investments in AralParker
                           CJSC represented by its note payable in a principal
                           amount of up to $50 million."

         SECTION 3. Amendment to Certain Covenants. The following provisions
shall be amended by this Fourth Supplemental Indenture as follows:

                           Section 3.1 Amendment to Section 4.07 (Restricted
                  Payments). Section 4.07 shall be amended by

                           (a) adding the following clause (w) to the second
                  paragraph of the section immediately before clause (y) : "(w)
                  any purchase, redemption or other acquisition or retirement,
                  in each case at a price less than par, of up to $75 million
                  aggregate principal amount of the Company's 5 1/2% convertible
                  Subordinated Notes due 2004 prior to their stated maturity;"
                  and adding "(w)," before the reference to "(y) and (z)" in
                  paragraph (c) of that section; and

                           (b) adding the words "and Affiliates" immediately
                  after "Unrestricted Subsidiaries" in clause (iii) of paragraph
                  (c) of that section and, in that same clause (iii), adding the
                  words "Affiliate or" immediately after the words "Unrestricted
                  Subsidiary or".

                           Section 3.2 Amendment to Section 4.10 (Asset Sales).
                  Section 4.10 shall be amended by adding the following proviso
                  to the end of the first paragraph of that section: "and
                  provided further, that the Company may engage in the sale or
                  transfer of properties or assets, including two drilling rigs
                  and related inventories and equipment and a contract with
                  Tengizchevroil, to AralParker CJSC, in consideration of a note
                  payable by AralParker CJSC in a principal amount of up to $50
                  million."

         SECTION 4. Effectiveness; Construction.

                           Section 4.1 Effectiveness. This Fourth Supplemental
                  Indenture shall become effective upon:

                           (a)      the execution and delivery of this Fourth
                                    Supplemental Indenture by the Company, the
                                    Subsidiary Guarantors and the Trustee; and

                           (b)      the delivery by the Company to the Trustee
                                    of the Opinion of Counsel and an Officers'
                                    Certificate as required pursuant to Sections
                                    11.04 and

                                      -2-
<PAGE>

                                    11.05 of the 1998 Indenture and addressing
                                    the matters required pursuant to such
                                    sections.

                           Section 4.2 Operative Date. The waivers and
                  amendments contained in this Fourth Supplemental Indenture
                  shall not become operative until the later of (i) the time at
                  which the Exchange Offer is consummated and (ii) the Company
                  has accepted a majority in aggregate principal amount of the
                  Notes outstanding in exchange for the New Notes. After this
                  Fourth Supplemental Indenture becomes effective, the Company
                  shall provide the notice required by Section 9.02 of the 1998
                  Indenture.

                           Section 4.3 Instruments To Be Read Together. All
                  terms and conditions in this Fourth Supplemental Indenture
                  shall form a part of the 1998 Indenture as fully and with the
                  same effect as if all such terms and conditions had been set
                  forth in the 1998 Indenture. The 1998 Indenture is hereby
                  ratified and confirmed and shall remain and continue in full
                  force and effect in accordance with its terms, as supplemented
                  by this Fourth Supplemental Indenture. The 1998 Indenture and
                  all supplements thereto, including this Fourth Supplemental
                  Indenture shall be read, taken and construed together as one
                  instrument.

         SECTION 5. Particular Representations and Covenants.

                           Section 5.1. Authority. The Company is duly
                  authorized by a resolution of its Board of Directors to
                  execute and deliver this Fourth Supplemental Indenture, and
                  all corporate action on its part required for the execution
                  and delivery of this Fourth Supplemental Indenture has been
                  duly and effectively taken.

                           Section 5.2. Correctness of Recitals. The Company
                  represents and warrants that all recitals and statements in
                  this Fourth Supplemental Indenture are true and correct.

         SECTION 6. Concerning the Trustee.

                           Section 6.1 Acceptance of Trusts. The Trustee accepts
                  the trusts hereunder and agrees to perform same, but only upon
                  the terms and conditions set forth in the Indenture.

                           Section 6.2 Responsibility for Recitals. The recitals
                  and statements contained in this Fourth Supplemental Indenture
                  shall be taken as recitals and statements of the Company, and
                  the Trustee assumes no responsibility for the correctness of
                  same. The Trustee makes no representations as to the validity
                  or sufficiency of this Fourth Supplemental Indenture, except
                  that the Trustee is duly authorized to execute and deliver it.

         SECTION 7. Miscellaneous Provisions.

                           Section 7.1 Counterparts. This Fourth Supplemental
                  Indenture may be executed in several counterparts, each of
                  which shall be deemed an original, but all of which together
                  shall constitute one instrument.

                                      -3-
<PAGE>

                           Section 7.2 Compliance with Trust Indenture Act. This
                  Fourth Supplemental Indenture shall be interpreted to comply
                  in every respect with the Trust Indenture Act of 1939, as
                  amended, (the "TIA"). If any provision of this Fourth
                  Supplemental Indenture limits, qualifies or conflicts with the
                  duties imposed by the TIA, the imposed duties shall control.

                           Section 7.3 Headings. The section headings herein are
                  for convenience only and shall not affect the construction
                  hereof.

                           Section 7.4 Binding Effect. All covenants and
                  agreements in this Fourth Supplemental Indenture by the
                  Company or by any of the Subsidiary Guarantors shall bind
                  their successors and assigns, whether so expressed or not.

                           Section 7.5 Governing Law. The internal laws of the
                  State of New York shall govern and be used to construe this
                  Fourth Supplemental Indenture.

                           Section 7.6 Continuation of 1998 Indenture. Except as
                  amended by this Fourth Supplemental Indenture, the terms and
                  provisions of the 1998 Indenture shall remain in full force
                  and effect.

                           Section 7.7 References to 1998 Indenture. From and
                  after the operative date referred to in Section 4.2 hereof,
                  all references in the 1998 Indenture to "this Indenture",
                  "hereof", "herein" or similar terms and all references to the
                  1998 Indenture in the Notes and other documents executed and
                  delivered in connection with the 1998 Indenture shall mean and
                  refer to the 1998 Indenture, as amended by this Fourth
                  Supplemental Indenture.

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

                           PARKER DRILLING COMPANY

                           By: /s/ James J. Davis
                              -----------------------------------------
                           Name:  James J. Davis
                           Title: Sr. Vice President-Finance and
                                  Chief Financial Officer

                           JPMORGAN CHASE BANK, as Trustee

                           By: /s/ Mauri J. Cowen
                              -----------------------------------------
                           Name: Mauri J. Cowen
                           Title: Vice President and Trust Officer

                           SUBSIDIARY GUARANTORS :

                           Parker Drilling Company of Oklahoma, Incorporated
                           Parker Drilling Company Limited (Nevada)
                           Parker Drilling Company Limited (Oklahoma)
                           Choctaw International Rig Corp.
                           Parker Drilling Company of New Guinea, Inc.

                                      -4-
<PAGE>

                           Parker Drilling Company North America, Inc.
                           Parker-VSE, Inc. (formerly Vance Systems
                                Engineering, Inc.)
                           DGH, Inc.
                           Parker Drilling Company International Limited
                           Parker USA Drilling Company (formerly
                                Parcan Limited)
                           Parker Technology, L.L.C.
                           Parker Technology, Inc.
                           Parker Drilling U.S.A. Ltd.
                           Parker Drilling Offshore Corporation (formerly
                                Hercules Offshore Corporation)
                           Parker Drilling Offshore International, Inc.
                           Anachoreta, Inc.
                           Pardril, Inc.
                           Parker Aviation, Inc.
                           Parker Drilling (Kazakstan), Ltd.
                           Parker Drilling Company of Niger
                           Parker North America Operations, Inc.
                           Selective Drilling Corporation
                           Universal Rig Service Corp.
                           Creek International Rig Corp.

                           By: /s/ David W. Tucker
                              -------------------------------------------------
                           Name:  David W. Tucker
                           Its:   Vice President & Treasurer

                           Parker Technology, L.L.C.

                           By: /s/ David W. Tucker
                              -------------------------------------------------
                           Name:  David W. Tucker
                           Its:   Vice President & Manager

                           Parker Drilling Offshore USA, L.L.C. (formerly
                                Mallard Bay Drilling, L.L.C.)

                           By: /s/ David W. Tucker
                              -------------------------------------------------
                           Name:  David W. Tucker
                           Its:   Treasurer & Manager

                           Parker Drilling Management Services, Inc.

                           By: /s/ David W. Tucker
                              -------------------------------------------------
                           Name:  David W. Tucker
                           Its:   President

                           Quail Tools, L.LP.

                           By: /s/ James J. Davis
                              -------------------------------------------------
                           Name:  James J. Davis
                           Its:   Vice President & Treasurer

                                      -5-

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