Exhibit 5.1

June 22, 2021

Diamond Offshore Drilling, Inc.

15415 Katy Freeway

Houston, Texas 77094

Ladies and Gentlemen:

We have acted as counsel to Diamond Offshore Drilling, Inc., a Delaware corporation (the “Company”), with respect to certain legal matters in connection with the preparation and filing on the date hereof by the Company with the Securities and Exchange Commission (the “Commission”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), of a registration statement on Form S-1 (the “Registration Statement”). The Registration Statement relates to the registration of 22,892,773 shares (the “Shares”) of the common stock, par value $0.0001 per share (“Common Stock”), of the Company to be offered and resold from time to time by the selling stockholders named in the Registration Statement under the heading “Selling Stockholders”. You have advised us that the Company issued the Shares pursuant to the Company’s Joint Chapter 11 Plan of Reorganization of Diamond Offshore Drilling, Inc. and Its Debtor Affiliates, as amended (the “Plan”), as approved and confirmed in an order (the “Confirmation Order”) entered by the United States Bankruptcy Court for the Southern District of Texas on April 8, 2021. The Shares may be sold from time to time as set forth in the Registration Statement, the prospectus contained therein (the “Prospectus”) and any amendments or supplements thereto. This opinion is being rendered in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the Securities Act.

For purposes of rendering this opinion, we have examined originals or copies (certified or otherwise identified to our satisfaction) of (i) the Registration Statement, (ii) the Prospectus, (iii) the Plan, (iv) the Confirmation Order, (v) the Company’s Third Amended and Restated Certificate of Incorporation (the “Restated Certificate”) and Second Amended and Restated Bylaws, (vi) certain resolutions of the Company’s Board of Directors approving the Registration Statement and (vii) such corporate records, agreements, documents and other instruments, and such certificates or comparable documents of public officials and of officers and representatives of the Company, and have made such inquiries of such officers and representatives, as we have deemed relevant and necessary as a basis for the opinions hereinafter set forth.

In such examination, we have assumed (i) the genuineness of all signatures, (ii) the legal capacity and competency of all natural persons, (iii) the authenticity of all documents submitted to us as originals, (iv) the conformity to original documents of all documents submitted to us as facsimile, electronic, certified, conformed or other copies and the authenticity of the originals of such documents, (v) that all records and other information made available to us by the Company on which we have relied are true, accurate and complete in all material respects, (vi) that each person signing in a representative capacity (other than on behalf of the Company) any document reviewed by us had authority to sign in such capacity, (vii) that the Registration Statement, and any amendments thereto (including, as applicable, all necessary post-effective amendments thereto), will have become effective under the Securities Act and comply with all applicable laws, (viii) that all Shares will be sold in compliance with federal and state securities laws and in the manner stated in the Registration Statement or any amendment thereto (including post-effective amendments), the Prospectus and any applicable prospectus supplement, and that all applicable provisions of the securities laws of the various jurisdictions in which the Shares may be offered and sold will have been complied with, and (ix) that each certificate from governmental officials reviewed by us is accurate, complete and authentic, and all official public records are accurate and complete.

Diamond Offshore Drilling, Inc. June 22, 2021 Page 2

As to all questions of fact material to these opinions, we have relied solely upon the above-referenced certificates or comparable documents and have not performed or had performed any independent research or investigation of public records as to the facts set forth therein and have assumed that certificates of or other comparable documents from public officials dated prior to the date hereof remain accurate as of the date hereof.

Based on the foregoing, and subject to the limitations, assumptions and qualifications stated herein, we are of the opinion that the Shares are validly issued, fully paid and nonassessable.

The opinions expressed herein are limited to the Delaware General Corporation Law (collectively, the “Applicable Laws”). No opinion is expressed as to the effect on the matters covered by this letter of the laws of (i) the State of Delaware other than the Applicable Laws or (ii) any jurisdiction other than the State of Delaware, whether in any such case applicable directly or through the Applicable Laws. We express no opinion regarding any federal or state securities laws or regulations or as to whether, or the extent to which, the laws of any particular jurisdiction apply to the subject matter hereof.

The Shares may be sold from time to time on a delayed or continuous basis, and the opinions expressed herein are rendered as of the date hereof and are based on existing law, which is subject to change. Where our opinions expressed herein refer to events to occur at a future date, we have assumed that there will have been no changes in the relevant law or facts between the date hereof and such future date. We do not undertake to advise you of any changes in the opinions expressed herein from matters that may hereafter arise or be brought to our attention or to revise or supplement such opinions should the present laws of any jurisdiction be changed by legislative action, judicial decision or otherwise. These opinions are expressed as of the date hereof unless otherwise expressly stated, and we disclaim any undertaking to advise you of any subsequent changes in the facts stated or assumed herein or of any subsequent changes in applicable laws.

Our opinions expressed herein are limited to the matters expressly stated herein and no opinion is implied or may be inferred beyond the matters expressly stated.

This letter may be relied upon by the Company and by persons entitled to rely upon it pursuant to the applicable provisions of the Securities Act and cannot be relied upon for any other purpose. We hereby consent to the use of this letter as an exhibit to the Registration Statement and to any and all references to our firm under the heading “Legal Matters” in the Prospectus. In giving this consent, we do not imply or admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission promulgated thereunder.

Very truly yours,

/s/ Duane Morris LLP