Exhibit 5.1

Gibson, Dunn & Crutcher LLP   811 Main Street Houston, TX 77002-6117 Tel 346.718.6600 www.gibsondunn.com

September 5, 2023

Patterson-UTI Energy, Inc.

10713 W. Sam Houston Pkwy N, Suite 800

Houston, Texas 77064

Re: Patterson-UTI Energy, Inc.

Registration Statement on Form S-3 (File No. 333-274345)

Ladies and Gentlemen:

We have examined the Registration Statement on Form S-3, File No. 333-274345 (the “Registration Statement”), of Patterson-UTI Energy, Inc., a Delaware corporation (the “Company”), filed with the Securities and Exchange Commission (the “Commission”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), and the prospectus and prospectus supplement with respect thereto, each dated September 5, 2023, in connection with the offering by the selling stockholder identified in the prospectus supplement of up to 34,900,000 shares of the Company’s common stock, par value $0.01 per share (the “Shares”).

In arriving at the opinion expressed below, we have examined originals, or copies certified or otherwise identified to our satisfaction as being true and complete copies of the originals, of such documents, records, certificates of officers of the Company and of public officials and other instruments as we have deemed necessary or advisable to enable us to render this opinion. In our examination, we have assumed without independent investigation the genuineness of all signatures, the legal capacity and competency of all natural persons, the authenticity of all documents submitted to us as originals and the conformity to original documents of all documents submitted to us as copies.

Based on the foregoing and in reliance thereon, and subject to the assumptions, exceptions, qualifications and limitations set forth herein, we are of the opinion that the Shares are validly issued, fully paid and non-assessable.

We render no opinion herein as to matters involving the laws of any jurisdiction other than the Delaware General Corporation Law (the “DGCL”). We are not admitted to practice in the State of Delaware; however, we are generally familiar with the DGCL as currently in effect and have made such inquiries as we consider necessary to render the opinion expressed above. This opinion is limited to the effect of the current state of the DGCL and the facts as they currently exist. We assume no obligation to revise or supplement this opinion in the event of future changes in such laws or the interpretations thereof or such facts.

Abu Dhabi • Beijing • Brussels • Century City • Dallas • Denver • Dubai • Frankfurt • Hong Kong • Houston • London • Los Angeles

Munich • New York • Orange County • Palo Alto • Paris • San Francisco • Singapore • Washington, D.C.

Patterson-UTI Energy, Inc.

September 5, 2023

Page 2

We consent to the filing of this opinion as an exhibit to the Registration Statement, and we further consent to the use of our name under the caption “Legal Matters” in the Registration Statement and the prospectus supplement. In giving these consents, we do not thereby 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/ Gibson, Dunn & Crutcher LLP