Exhibit 5.1

2555 Grand Blvd.

Kansas City

Missouri 64108

t 816.474.6550

f 816.421.5547

September 23, 2020

O’Reilly Automotive, Inc.

233 South Patterson

Springfield, Missouri 65802

Dear Ladies and Gentlemen:

We have been retained as special Missouri counsel for O’Reilly Automotive, Inc., a Missouri corporation (“O’Reilly”) in connection with the public offering of $500,000,000 aggregate principal amount of O’Reilly’s 1.750% Senior Notes due 2031 (the “Notes”), issued pursuant to an indenture, dated May 20, 2019 (the “Base Indenture”), as supplemented by the third supplemental indenture, dated as of September 23, 2020 (together with the Base Indenture, the “Indenture”), by and between O’Reilly and U.S. Bank National Association. O’Reilly entered into an underwriting agreement, dated as of September 9, 2020 (the “Underwriting Agreement”), with BofA Securities, Inc. and Wells Fargo Securities, LLC, as representatives of the several underwriters named in Schedule I of the Underwriting Agreement (the “Underwriters”) relating to the sale by O’Reilly to the Underwriters of the Notes.

We have reviewed copies of the Indenture, the Notes, and the Underwriting Agreement. We have reviewed the Good Standing Certificate with respect to O’Reilly issued by the Secretary of State of Missouri dated September 8, 2020. We have also reviewed the organizational documents of O’Reilly. We have also examined copies of resolutions adopted by the board of directors of O’Reilly on September 3, 2020, and by the pricing committee of the board of directors of O’Reilly on September 4, 2020, each certified by the Secretary of O’Reilly as of September 23, 2020.

We have assumed for purposes of this opinion that: (i) all certifications of public officials and officers of O’Reilly concerning factual matters are accurate and complete; (ii) all signatures are genuine, the documents submitted to us as originals are authentic and the documents submitted to us as copies conform to the originals; (iii) the statements, recitals, representations and warranties as to matters of fact set forth in the Indenture are accurate and complete; (iv) the Notes have been duly authenticated, issued and delivered in accordance with the terms of the Indenture and the Underwriting Agreement; and (v) each of the Underwriting Agreement and the Indenture has been duly authorized, executed and delivered by all parties thereto (other than O’Reilly).

As to facts material to this opinion, we have, with your permission, relied upon certificates and oral and written statements of officers of O’Reilly and on the representations and statements of fact made in the Indenture and Underwriting Agreement. Except to the extent expressly set forth herein, we have not undertaken any independent investigation to determine the existence or absence of any fact. We are not generally familiar with the business or operations of O’Reilly and no inference as to our knowledge of the existence or absence of any fact should be drawn from our representation of O’Reilly or the rendering of the opinions set forth below.

CHICAGO | DENVER | HOUSTON | KANSAS CITY | LONDON | LOS ANGELES | MIAMI | ORANGE COUNTY | PHILADELPHIA | SAN FRANCISCO | SEATTLE | TAMPA | WASHINGTON, D.C.

September 23, 2020

Page 2

Based on the foregoing and in reliance thereon and on the assumptions and subject to the qualifications and limitations set forth in this opinion, we are of the opinion that:

Our opinions are based on the assumptions (upon which we have relied with your consent) and subject to the qualifications and limitations set forth in this letter, including the following:

This opinion is furnished to you for your benefit in connection with the filing of the Prospectus Supplement (to Prospectus, dated March 1, 2019), dated September 9, 2020, relating to the offering of the Notes filed with the Commission pursuant to Rule 424(b) of the Rules and Regulations under the Securities Act.

September 23, 2020

Page 3

We also hereby consent to the filing of this opinion with the Commission as an exhibit to O’Reilly’s Current Report on Form 8-K being filed on the date hereof and incorporated by reference into the Registration Statement pursuant to Item 16 of Form S-3 and Item 601(b)(5) of Regulation S-K promulgated under the Securities Act. We also consent to the reference to our firm under the heading “Legal Matters” in the Registration Statement solely with respect to the laws of the State of Missouri as they apply to O’Reilly. In giving this consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission. No expansion of our opinions may be made by implication or otherwise. We express no opinion other than the opinions set forth herein.