SIXTH SUPPLEMENTAL INDENTURE

Exhibit 4.2

SIXTH SUPPLEMENTAL INDENTURE

between

DIAMOND OFFSHORE DRILLING, INC.

and

THE BANK OF NEW YORK MELLON,

as Trustee

Dated as of

May 4, 2009

TABLE OF CONTENTS

Page

ARTICLE 1
The 2019 Notes

ARTICLE 2
Amendments to the Indenture

ARTICLE 3
Miscellaneous Provisions

DIAMOND OFFSHORE DRILLING, INC.

SIXTH SUPPLEMENTAL INDENTURE

     THIS SIXTH SUPPLEMENTAL INDENTURE, dated as of May 4, 2009, between Diamond Offshore Drilling, Inc., a Delaware corporation (the “ Company ”), and The Bank of New York Mellon (formerly known as The Bank of New York) (as successor under the Indenture to The Chase Manhattan Bank), a banking corporation organized and existing under the laws of the State of New York (the “ Trustee ”).

WITNESSETH

     WHEREAS, the Company has heretofore executed and delivered to the Trustee an Indenture, dated as of February 4, 1997 (the “ Indenture ”), providing for the issuance from time to time of its debentures, notes, bonds or other evidences of indebtedness in one or more fully registered series;

     WHEREAS, Section 901(5) of the Indenture provides that the Company and the Trustee may from time to time enter into one or more indentures supplemental thereto to establish the form or terms of Securities of a new series;

     WHEREAS, Sections 901(2) and 901(7) of the Indenture permit the execution of supplemental indentures without the consent of any Holders to add to the covenants of the Company for the benefit of, and to add any additional Events of Default with respect to, all or any series of Securities;

     WHEREAS, Section 301 of the Indenture provides that the Company may enter into supplemental indentures to establish the terms and provisions of a series of Securities issued pursuant to the Indenture;

     WHEREAS, the Company desires to issue 5.875% Senior Notes due May 1, 2019 (the “ 2019 Notes ”), a new series of Security, the issuance of which was authorized by resolution of the Board of Directors of the Company, dated April 22, 2009, and by a unanimous written consent of the Securities Committee of the Board of Directors of the Company, dated April 29, 2009;

     WHEREAS, the Company, pursuant to the foregoing authority, proposes in and by this Sixth Supplemental Indenture to supplement and amend in certain respects the Indenture insofar as it will apply only to the 2019 Notes (and not to any other series); and

     WHEREAS, all things necessary have been done to make the 2019 Notes, when executed by the Company and authenticated and delivered hereunder and duly issued by the Company, the valid and legally binding obligations of the

Company, and to make this Sixth Supplemental Indenture a valid and legally binding agreement of the Company, in accordance with their and its terms.

     NOW THEREFORE:

     In consideration of the premises provided for herein, the Company and the Trustee mutually covenant and agree for the equal and proportionate benefit of all Holders of the 2019 Notes as follows:

ARTICLE 1
The 2019 Notes

     Section 1.01 . Designation of 2019 Notes; Establishment of Form. There shall be a series of Securities designated “5.875% Senior Notes due May 1, 2019” of the Company, and the form thereof shall be substantially as set forth in Annex A hereto, which is incorporated into and shall be deemed a part of this Sixth Supplemental Indenture, with such appropriate insertions, omissions, substitutions and other variations as are required or permitted by the Indenture, and may have such letters, numbers or other marks of identification and such legends or endorsements placed thereon as may be required to comply with the rules of any securities exchange or as may, consistently herewith, be determined by the officers of the Company executing such 2019 Notes, as evidenced by their execution of the 2019 Notes.

     (a)  Global Securities . All of the 2019 Notes shall be issued initially in the form of one or more notes in registered, global form without interest coupons, (collectively, the “ Global Securities ”). The Global Securities shall be deposited on behalf of the purchasers of the 2019 Notes represented thereby with the Trustee, at its Corporate Trust Office, as Securities Custodian for the depositary, The Depository Trust Company (the “ DTC ”) (such depositary, or any successor thereto, being hereinafter referred to as the “ Depositary ”), and registered in the name of its nominee, Cede & Co., in each case for credit to an account of a direct or indirect participant in the DTC (including, if applicable, Euroclear System or Clearstream Banking Luxembourg), duly executed by the Company and authenticated by the Trustee as hereinafter provided. The aggregate principal amount of a Global Security may from time to time be increased or decreased by adjustments made on the records of the Securities Custodian as hereinafter provided, subject in each case to compliance with the Applicable Procedures.

     Each Global Security shall represent such of the Outstanding 2019 Notes as shall be specified therein and each shall provide that it shall represent the aggregate principal amount of Outstanding 2019 Notes from time to time endorsed thereon and that the aggregate principal amount of Outstanding 2019 Notes represented thereby may from time to time be reduced or increased, as

appropriate, to reflect exchanges or redemptions of such 2019 Notes. Any endorsement of a Global Security to reflect the amount of any increase or decrease in the principal amount of Outstanding 2019 Notes represented thereby shall be made by the Securities Custodian in accordance with the standing instructions and procedures existing between the Depositary and the Securities Custodian.

     Neither any members of, or participants in, the Depositary (“ Agent Members ”) nor any other Persons on whose behalf Agent Members may act shall have rights under this Sixth Supplemental Indenture with respect to any Global Security held in the name of the Depositary or any nominee thereof, or under the Global Security, and the Depositary (including, for this purpose, its nominee) may be treated by the Company, the Trustee and any agent of the Company or the Trustee as the absolute owner and Holder of such Global Security for all purposes whatsoever. Notwithstanding the foregoing, nothing herein shall (A) prevent the Company, the Trustee or any agent of the Company or the Trustee from giving effect to any written certification, proxy or other authorization furnished by the Depositary or (B) impair, as between the Depositary, its Agent Members and any other Person on whose behalf an Agent Member may act, the operation of customary practices governing the exercise of the rights of a Holder of any 2019 Notes.

     (b)  Certified Securities . Certificated Securities shall be issued only under the limited circumstances provided in Section 1.02(a) hereof.

     (c)  Paying Agent . The Company shall maintain an office or agency where 2019 Notes may be presented for payment (“ Paying Agent ”). The Company shall enter into an appropriate agency agreement with a Paying Agent. The agreement shall implement the provisions of this Sixth Supplemental Indenture that relate to such agent. The Company shall notify the Trustee of the name and address of any such agent. If the Company fails to maintain a Paying Agent, the Trustee shall act as such and shall be entitled to appropriate compensation therefor pursuant to Section 607 of the Indenture. The Company or any Subsidiary or an Affiliate of either of them may act as Paying Agent. The Company initially appoints the Trustee as Paying Agent in connection with the 2019 Notes.

     (d)  Similar Debt Securities. Any additional Securities having similar terms to the 2019 Notes, together with the 2019 Notes will constitute a single series of Securities under the Indenture if such additional Securities are fungible with the 2019 Notes for United States federal income tax purposes.

Section 1.02 Transfer and Exchange.

     (a)  Transfer and Exchange of Global Securities .

          (1)  Certificated Securities . Certificated Securities shall be issued in exchange for interests in the Global Securities only if (i) the Depositary notifies the Company that it is unwilling or unable to continue as depositary for the Global Securities or if it at any time ceases to be a “clearing agency” registered under the Exchange Act if so required by applicable law or regulation and a successor depositary is not appointed by the Company within 90 days, (ii) the Company at any time and in its sole discretion determines not to have the 2019 Notes represented by a Global Security, or (iii) an Event of Default has occurred and is continuing. In each case, the Company shall execute, and the Trustee shall, upon receipt of a Company Order (which the Company agrees to deliver promptly), authenticate and deliver Certificated Securities in an aggregate principal amount equal to the principal amount of such Global Securities in exchange therefor. Certificated Securities issued in exchange for beneficial interests in Global Securities shall be registered in such names and shall be in such authorized denominations as the Depositary, pursuant to instructions from its direct or indirect participants or otherwise, shall instruct the Trustee. The Trustee shall deliver or cause to be delivered such Certificated Securities to the persons in whose names such Securities are so registered. Such exchange shall be effected in accordance with the Applicable Procedures. Nothing herein shall require the Trustee to communicate directly with beneficial owners, and the Trustee shall in connection with any transfers hereunder be entitled to rely on instructions received through the registered Holder.

          In the event that Certificated Securities are issued in exchange for beneficial interests in Global Securities in accordance with the foregoing paragraph and, thereafter, the events or conditions specified in this Section 1.02(a)(1) which required such exchange shall have ceased to exist, the Company shall mail notice to the Trustee and to the Holders stating that Holders may exchange Certificated Securities for interests in Global Securities by complying with the procedures set forth in this Indenture and briefly describing such procedures and the events or circumstances requiring that such notice be given.

          (2) Notwithstanding any other provisions of this Indenture, a Global Security may not be transferred, except as a whole by the Depositary to a nominee of the Depositary or by a nominee of the Depositary to the Depositary or another nominee of the Depositary or by the Depositary or any such nominee to a successor Depositary or a nominee of such successor Depositary. Nothing in this Section 1.02(a)(2) shall prohibit or render ineffective any transfer of a beneficial interest in a Global Security effected in accordance with the other provisions of this Section 1.02.

     (b)  Restrictions on Transfer of a Beneficial Interest in a Global Security for a Certificated Security . A beneficial interest in a Global Security may not be exchanged for a Certified Security except under the limited circumstances provided in Section 1.02(a) hereof and upon satisfaction of the requirements set

forth below. Upon receipt by the Trustee of a request in the form satisfactory to the Trustee from the Depositary or its nominee on behalf of a person having a beneficial interest in a Global Security to register the transfer of all or a portion of such beneficial interest in accordance with Applicable Procedures for a Certificated Security, together with:

          (1) written instructions to the Trustee to make, or direct the Security Registrar to make, an adjustment on its books and records with respect to such Global Security to reflect a decrease in the aggregate principal amount of the 2019 Notes represented by the Global Security, such instructions to contain information regarding the Depositary account to be credited with such decrease; and

          (2) if the Company or the Trustee so requests, a customary opinion of counsel, certificates and other information reasonably acceptable to them,

then the Trustee shall cause, or direct the Security Registrar to cause, in accordance with the standing instructions and procedures existing between the Depository and the Security Registrar, the aggregate principal amount of 2019 Notes represented by the Global Security to be decreased by the aggregate principal amount of the Certificated Security to be issued, shall authenticate and deliver such Certificated Security and shall debit or cause to be debited to the account of the Person specified in such instructions a beneficial interest in the Global Security equal to the principal amount of the Certificated Security so issued.

     (c)  Transfer and Exchange of Certificated Securities . When Certificated Securities are presented by a Holder to a Security Registrar with a request:

          (1) to register the transfer of the Certificated Securities to a person who will take delivery thereof in the form of Certificated Securities only; or

          (2) to exchange such Certificated Securities for an equal principal amount of Certificated Securities of other authorized denominations;

such Security Registrar shall register the transfer or make the exchange as requested; provided, however , that the Certificated Securities presented or surrendered for register of transfer or exchange shall be duly endorsed or accompanied by a written instrument of transfer in accordance with the fifth paragraph of Section 305 of the Indenture.

     (d)  Transfers of Certificated Securities for Beneficial Interest in Global Securities. If Certificated Securities are presented by a Holder to a Security Registrar with a request:

          (1) to register the transfer of such Certificated Securities to a person who will take delivery thereof in the form of a beneficial interest in a Global Security; or

          (2) to exchange such Certificated Securities for an equal principal amount of beneficial interests in a Global Security, which beneficial interests will be owned by the Holder transferring such Certificated Securities;

the Security Registrar shall register the transfer or make the exchange as requested by canceling such Certificated Security and causing, or directing the Securities Custodian to cause, the aggregate principal amount of the applicable Global Security to be increased accordingly and, if no such Global Security is then outstanding, the Company shall issue and the Trustee shall authenticate and deliver a new Global Security; provided, however, that the Certificated Securities presented or surrendered for registration of transfer or exchange shall be duly endorsed or accompanied by a written instrument of transfer in accordance with the fifth paragraph of Section 305 of the Indenture.

     (e)  Transfers to the Company. Nothing in this Indenture or in the Securities shall prohibit the sale or other transfer of any Securities (including beneficial interests in Global Securities) to the Company or any of its Subsidiaries. Any Securities purchased by the Company shall thereupon be canceled in accordance with Section 309 of the Indenture.

Section 103 Amount.

     Section 1.02 . Amount. The Trustee shall authenticate and deliver 2019 Notes for original issue in an aggregate principal amount of up to $500,000,000 upon a Company Order for the authentication and delivery of 2019 Notes, without any further action by the Company. The aggregate principal amount of 2019 Notes that may be authenticated and delivered under the Indenture may not exceed the amount set forth in the foregoing sentence, except for 2019 Notes authenticated and delivered upon registration of transfer of, or in exchange for, or in lieu of, other 2019 Notes pursuant to Section 1.02 of this Sixth Supplemental Indenture or Section 204, 304, 305, 306, 906 or 1107 of the Indenture.

     Section 1.03 . Regular Interest. The principal of the 2019 Notes shall bear interest at the rate of 5.875% per annum from May 4, 2009 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, payable semiannually in arrears on May 1 and November 1 of each year, commencing November 1, 2009, to the Persons in whose names the 2019 Notes

are registered at the close of business on the April 15 or October 15 (whether or not a Business Day), as the case may be, next preceding such Interest Payment Date. Interest on the 2019 Notes will be computed on the basis of a 360-day year comprised of twelve 30-day months.

     Section 1.04 . Denominations. The 2019 Notes shall be in fully registered form without coupons in denominations of $2,000 of principal amount or any integral multiple of $1,000 in excess thereof.

     Section 1.05 . Place of Payment. The Place of Payment for the 2019 Notes and the place or places where the 2019 Notes may be surrendered for registration of transfer, exchange or redemption and where notices may be given to the Company in respect of the 2019 Notes is at the office of the Trustee in New York, New York and at the agency of the Trustee maintained for that purpose at the office of the Trustee; provided, however, that payment of interest may be made at the option of the Company by check mailed to the address of the Person entitled thereto as such address shall appear in the Security Register (as defined in the Indenture).

     Section 1.06 . Redemption. (a) There shall be no sinking fund for the retirement of the 2019 Notes.

     (b) The Company, at its option, may redeem the 2019 Notes in accordance with the provisions and at the Redemption Price set forth under the captions “Optional Redemption” and “Notice of Redemption” in the 2019 Notes and in accordance with the provisions of the Indenture, including, without limitation, Article Eleven.

     Section 1.07 . Stated Maturity. The date on which the principal of the 2019 Notes is due and payable, unless accelerated, redeemed or required to be repurchased pursuant to the Indenture, shall be May 1, 2019.

     Section 1.08 . Discharge of Liability on 2019 Notes. The 2019 Notes may be discharged by the Company in accordance with the provisions of Article Four of the Indenture, as amended by Section 2.05 hereof.

     Section 1.09 . Other Terms of 2019 Notes. Without limiting the foregoing provisions of this Article 1, the terms of the 2019 Notes shall be as set forth in the form of the 2019 Notes set forth in Annex A hereto and as provided in the Indenture.

ARTICLE 2
Amendments to the Indenture

     Section 2.01 . Amendments Applicable Only to 2019 Notes. The amendments contained herein shall apply to the 2019 Notes only and not to any other series of Security issued under the Indenture, and any covenants provided herein are expressly being included solely for the benefit of the 2019 Notes and not for the benefit of any other series of Security issued under the Indenture. These amendments shall be effective for so long as there remain any 2019 Notes Outstanding.

     Section 2.02 . Definitions. Section 101 of the Indenture is hereby amended, subject to Section 2.01 hereof and with respect to the 2019 Notes only, by inserting or restating, as the case may be, in their appropriate alphabetical position, the following definitions:

     “ Adjusted Treasury Rate ” means, with respect to any Redemption Date, the rate per annum equal to the semi-annual equivalent yield to maturity of the Comparable Treasury Issue, assuming a price for the Comparable Treasury Issue (expressed as a percentage of the principal amount) equal to the Comparable Treasury Price for that redemption date. The Adjusted Treasury Rate will be calculated on the third business day preceding the Redemption Date.

     “ Agent Members ” has the meaning specified in Section 1.01(a).

     “ Applicable Procedures ” means, with respect to any transfer or exchange of beneficial ownership interests in a Global Security, the rules and procedures that are applicable to such transfer or exchange of the Depositary and its direct or indirect participants, including, if applicable, those of Euroclear Bank S.A./N.V. (as operator of the Euroclear system) and Clearstream Banking Luxembourg, which may change from time to time.

     “ Capital Stock ” or “ capital stock ” of any Person means any and all shares, interests, partnership interests, participations, rights or other equivalents (however designated) of equity interests (however designated) issued by that Person.

     “ Certificated Security ” means a Security that is in substantially the form attached hereto as Annex A and that does not include the information or the schedule called for by footnotes 1, 2 and 3 thereof.

     “ Comparable Treasury Issue ” means the U.S. Treasury security selected by the applicable Quotation Agent as having a maturity comparable to the remaining term of the 2019 Notes to be redeemed that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing

new issues of corporate debt securities of comparable maturity to the remaining term of those 2019 Notes.

     “ Comparable Treasury Price ” means, with respect to any Redemption Date, (A) the average of four Reference Treasury Dealer Quotations for that redemption date, after excluding the highest and lowest of those Reference Treasury Dealer Quotations, or (B) if the Company obtains fewer than four such Reference Treasury Dealer Quotations, the average of all of those quotations.

     “ Consolidated Net Tangible Assets ” means the total amount of assets (less applicable reserves and other properly deductible items) after deducting (1) all current liabilities (excluding the amount of those which are by their terms extendable or renewable at the option of the obligor to a date more than 12 months after the date as of which the amount is being determined) and (2) all goodwill, tradenames, trademarks, patents, unamortized debt discount and expense and other like intangible assets, all as set forth on the most recent balance sheet of the Company and its consolidated subsidiaries and determined in accordance with generally accepted accounting principles.

     “ Consolidated Net Worth ” means, at any time, the Net Worth of the Company and its Subsidiaries on a consolidated basis determined in accordance with GAAP.

     “ Corporate Trust Office ” means the principal office of the Trustee in New York, New York, at which at any particular time its corporate trust business shall be principally administered, which office at the date hereof is located at 101 Barclay Street, Floor 8W, New York, New York, 10286,

     “ Depositary ” has the meaning specified in Section 1.01(a).

     “ DTC ” has the meaning specified in Section 1.01(a).

     “ Exchange Act ” means the Securities Exchange Act of 1934, as amended, or any successor statute.

     “ Funded Debt ” means indebtedness of the Company or a Subsidiary owning Restricted Property maturing by its terms more than one year after its creation and indebtedness classified as long term debt under generally accepted accounting principles, and in each case ranking at least pari passu with the Securities.

     “ GAAP ” means generally accepted accounting principles as in effect on the date of determination in the United States.

     “ Global Security ” means a permanent Global Security that is in substantially the form attached hereto as Annex A and that includes the

information and schedule called for by footnotes 1, 2 and 3 thereof and which is deposited with the Depositary or the Securities Custodian and registered in the name of the Depositary or its nominee.

     “ Indenture ” has the meaning specified in the recitals.

     “ Issue Date ” of any 2019 Notes means the date on which the 2019 Notes were originally issued or deemed issued as set forth on the face of the 2019 Notes.

     “ Lien ” means any mortgage, pledge, lien, encumbrance, charge or security interest.

     “ Net Worth ” means, at any time with respect to the Company or a Subsidiary thereof, the net worth of the Company or such Subsidiary, as the case may be, determined in accordance with GAAP.

     “ Quotation Agent ” means the Reference Treasury Dealer appointed by the Company for the 2019 Notes.

     “ Reference Treasury Dealer ” means: (A) Goldman, Sachs & Co. and J.P. Morgan Securities Inc. and their successors; provided that, if any ceases to be a primary U.S. Government securities dealer (“ Primary Treasury Dealer ”), the Company will substitute another Primary Treasury Dealer; and (B) any other Primary Treasury Dealers selected by the Company.

     “ Reference Treasury Dealer Quotation ” means, with respect to each Reference Treasury Dealer and any Redemption Date, the average, as determined by the Trustee, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Trustee by such Reference Treasury Dealer at 5:00 p.m. (New York City time) on the third Business Day preceding that Redemption Date.

     “ Restricted Property ” means (1) any drilling rig or drillship which is leased by the Company or any Subsidiary as a lessee, or greater than a 50% interest in which is owned by the Company or any Subsidiary, and which is used for drilling offshore oil and gas wells, which, in the opinion of the Board of Directors, is of material importance to the business of the Company and its Subsidiaries taken as a whole, but no such drilling rig or drillship, or portion thereof, shall be deemed of material importance if its net book value is less than 2% of Consolidated Net Tangible Assets, or (2) any shares of capital stock or indebtedness of any Subsidiary owning any such drilling rig or drillship.

     “ Sale and Leaseback Transaction ” means any arrangement with any Person pursuant to which the Company or any Subsidiary leases any Restricted Property that has been or is to be sold or transferred by the Company or the

Subsidiary to such Person, other than (1) leases for a term, including renewals at the option of the lessee, of not more than five years, (2) leases between the Company and a Subsidiary or between Subsidiaries, (3) leases of a Restricted Property executed by the time of, or within 12 months after the latest of, the acquisition, the completion of construction or improvement, or the commencement of commercial operation of the Restricted Property, and (4) arrangements pursuant to any provision of law with an effect similar to the former Section 168(f)(8) of the Internal Revenue Code of 1954.

     “ Securities ” means any securities authenticated and delivered under the Indenture, as the same may be amended or supplemented, including 2019 Notes.

     “ Securities Custodian ” means the Trustee, as custodian with respect to the Securities in global form, or any successor thereto.

     “ Significant Subsidiary ” means any Subsidiary, the Net Worth of which represents more than 10% of the Consolidated Net Worth of the Company and its Subsidiaries.

     “ 2019 Notes ” has the meaning specified in the recitals.

     “ Value ” means, with respect to a Sale and Leaseback Transaction, an amount equal to the present value of the lease payments with respect to the term of the lease remaining on the date as of which the amount is being determined, without regard to any renewal or extension options contained in the lease (including the effective interest rate on any original issue discount Securities), which are outstanding on the effective date of such Sale and Leaseback Transaction and which have the benefit of Section 1010.

     Section 2.03 . Registration, Registration of Transfer and Exchange. The Indenture is hereby amended, subject to Section 2.01 hereof and with respect to the 2019 Notes only, by replacing the seventh paragraph of Section 305 with the following paragraph:

     The Company shall not be required (i) to issue, register the transfer of or exchange the Securities of any series during a period beginning at the opening of business 15 days before the day of the mailing of a notice of redemption of Securities of that series selected for redemption and ending at the close of business on the day of such mailing or (ii) to register the transfer of or e