Filed by ONEOK, Inc. pursuant to

Rule 425 under the Securities Act of 1933

and deemed filed pursuant to Rule 14a-12

under the Securities Exchange Act of 1934

Subject Company: Magellan Midstream Partners, L.P.

Commission File No. 001-16335

Date: July 25, 2023

Subject: Message From Pierce Norton and Aaron Milford: Filing of Our Joint Definitive Proxy Statement

To All ONEOK and Magellan Employees:

Today marks the accomplishment of another critical milestone in our journey toward Day 1 as a combined company – the filing of our joint definitive proxy statement with the U.S. Securities and Exchange Commission. With this action completed, ONEOK and Magellan will now begin soliciting votes in favor of the transaction. On September 21, 2023, each company will hold its own respective special meeting to allow ONEOK shareholders and Magellan unitholders to vote on, and approve, the transaction. ONEOK’s meeting will be held at 9 a.m. CT and Magellan’s will be held at 10 a.m. CT.

If you are a ONEOK shareholder or Magellan unitholder, your vote is important no matter how many shares or units you own. As detailed in the proxy materials, both the ONEOK and Magellan Boards of Directors unanimously agree this merger makes sense and creates more value for stakeholders. It is our strong belief that we are better together and every vote counts!

Some highlights of the transaction include:

We invite you to read the ONEOK and Magellan press releases. If you are a shareholder or unitholder, you soon will receive information in the mail about how to vote. Be on the lookout for that information.

We also invite you to continue to reference ONEOK’s and Magellan’s respective intranets for information about the transaction and integration, including FAQs that have been updated with information about the definitive joint proxy filing and the overview of the integration process.

We now are one step closer to completing the transaction, which remains on track to close in the third quarter 2023. As we have said before, it remains business as usual for both companies as we work toward close – we remain two separate entities and we must continue our important work to deliver for our customers.

We have much to look forward to as we build on strong momentum and become ONE organization.

Sincerely,

Pierce and Aaron

ONEOK shareholders who need assistance in completing the proxy card or voting instruction form or have questions regarding the ONEOK special meeting may contact ONEOK’s proxy solicitor, Innisfree M&A Incorporated, at 877-750-9499.

Magellan unitholders who need assistance in completing the proxy card or voting instruction form or have questions regarding the Magellan special meeting may contact either of Magellan’s proxy solicitors, Morrow Sodali, LLC, at 800-662-5200 or MMP@info.morrowsodali.com or MacKenzie Partners, Inc. by phone at 800-322-2885 or 212-929-5500 or by email at proxy@mackenziepartners.com.

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This communication contains “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. All statements, other than statements of historical fact, included in this communication that address activities, events or developments that ONEOK, Inc. (NYSE: OKE) (“ONEOK”) or Magellan Midstream Partners, L.P. (NYSE: MMP) (“Magellan”) expects, believes or anticipates will or may occur in the future are forward-looking statements. Words such as “estimate,” “project,” “predict,” “believe,” “expect,” “anticipate,” “potential,” “create,” “intend,” “could,” “would,” “may,” “plan,” “will,” “guidance,” “look,” “goal,” “future,” “build,” “focus,” “continue,” “strive,” “allow” or the negative of such terms or other variations thereof and words and terms of similar substance used in connection with any discussion of future plans, actions, or events identify forward-looking statements. However, the absence of these words does not mean that the statements are not forward-looking. These forward-looking statements include, but are not limited to, statements regarding the proposed transaction between ONEOK and Magellan (the “Proposed Transaction”), the expected closing of the Proposed Transaction and the timing thereof and as adjusted descriptions of the post-transaction company and its operations, strategies and plans, integration, debt levels and leverage ratio, capital expenditures, cash flows and anticipated uses thereof, synergies, opportunities and anticipated future performance, including maintaining current ONEOK management, enhancements to investment-grade credit profile, an expected accretion to earnings and free cash flow, dividend payments and potential share repurchases, increase in value of tax attributes and expected impact on EBITDA. Information adjusted for the Proposed Transaction should not be considered a forecast of future results. There are a number of risks and uncertainties that could cause actual results to differ materially from the forward-looking statements included in this communication. These include the risk that ONEOK’s and Magellan’s businesses will not be integrated successfully; the risk that cost savings, synergies and growth from the Proposed Transaction may not be fully realized or may take longer to realize than expected; the risk that the credit ratings of the combined company or its subsidiaries may be different from what the companies expect; the possibility that shareholders of ONEOK may not approve the issuance of new shares of ONEOK common stock in the Proposed Transaction or that unitholders of Magellan may not approve the Proposed Transaction; the risk that a condition to closing of the Proposed Transaction may not be satisfied, that either party may terminate the merger agreement or that the closing of the Proposed Transaction might be delayed or not occur at all; potential adverse reactions or changes to business or employee relationships, including those resulting from the announcement or completion of the Proposed Transaction; the occurrence of any other event, change or other circumstances that could give rise to the termination of the merger agreement relating to the Proposed Transaction; the risk that ONEOK may not be able to secure the debt financing necessary to fund the cash consideration required for the Proposed Transaction; the risk that changes in ONEOK’s capital structure and governance could have adverse effects on the market value of its securities; the ability of ONEOK and Magellan to retain customers and retain and hire key personnel and maintain relationships with their suppliers and customers and on ONEOK’s and Magellan’s operating results and business generally; the risk the Proposed Transaction could distract management from ongoing business operations or cause ONEOK and/or Magellan to incur substantial costs; the risk of any litigation relating to the Proposed Transaction; the risk that ONEOK may be unable to reduce expenses or access financing or liquidity; the impact of the COVID-19 pandemic, any related economic downturn and any related substantial decline in commodity prices; the risk of changes in governmental regulations or enforcement practices, especially with respect to environmental, health and safety matters; and other important factors that could cause actual results to differ materially from those projected. All such factors are difficult to predict and are beyond ONEOK’s or Magellan’s control, including those detailed in the joint proxy statement/prospectus (as defined below). All forward-looking statements are based on assumptions that ONEOK and Magellan believe to be reasonable but that may not prove to be accurate. Any forward-looking statement speaks only as of the date on which such statement is made, and neither ONEOK nor Magellan undertakes any obligation to correct or update any forward-looking statement, whether as a result of new information, future events or otherwise, except as required by applicable law. Readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof.

IMPORTANT ADDITIONAL INFORMATION AND WHERE TO FIND IT

In connection with the Proposed Transaction, on July 25, 2023, ONEOK and Magellan each filed with the Securities and Exchange Commission (the “SEC”) a definitive joint proxy statement/prospectus (the “joint proxy statement/prospectus”), and each party will file other documents regarding the Proposed Transaction with the SEC. Each of ONEOK and Magellan commenced mailing copies of the joint proxy statement/prospectus to shareholders of ONEOK and unitholders of Magellan, respectively, on or about July 25, 2023. This communication is not a substitute for the joint proxy statement/prospectus or for any other document that ONEOK or Magellan has filed or may file in the future with the SEC in connection with the Proposed Transaction. INVESTORS AND SECURITY HOLDERS OF ONEOK AND MAGELLAN ARE URGED TO CAREFULLY AND THOROUGHLY READ THE JOINT PROXY STATEMENT/PROSPECTUS, INCLUDING ALL AMENDMENTS AND SUPPLEMENTS THERETO, AND OTHER RELEVANT DOCUMENTS FILED OR THAT WILL BE FILED BY ONEOK AND MAGELLAN WITH THE SEC BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT ONEOK AND MAGELLAN, THE PROPOSED TRANSACTION, THE RISKS RELATED THERETO AND RELATED MATTERS.

Investors can obtain free copies of the joint proxy statement/prospectus and other relevant documents filed by ONEOK and Magellan with the SEC through the website maintained by the SEC at www.sec.gov. Copies of documents filed with the SEC by ONEOK, including the joint proxy statement/prospectus, are available free of charge from ONEOK’s website at www.oneok.com under the “Investors” tab. Copies of documents filed with the SEC by Magellan, including the joint proxy statement/prospectus, are available free of charge from Magellan’s website at www.magellanlp.com under the “Investors” tab.

NO OFFER OR SOLICITATION

This communication is not intended to and shall not constitute an offer to sell or the solicitation of an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offer of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended.

PARTICIPANTS IN THE SOLICITATION

ONEOK and certain of its directors, executive officers and other members of management and employees, Magellan, and certain of the directors, executive officers and other members of management and employees of Magellan GP, LLC, which manages the business and affairs of Magellan, may be deemed to be participants in the solicitation of proxies from ONEOK’s shareholders and the solicitation of proxies from Magellan’s unitholders, in each case with respect to the Proposed Transaction. Information about ONEOK’s directors and executive officers is available in ONEOK’s Annual Report on Form 10-K for the 2022 fiscal year filed with the SEC on February 28, 2023 and its definitive proxy statement for the 2023 annual meeting of shareholders filed with the SEC on April 5, 2023, and in the joint proxy statement/prospectus. Information about Magellan’s directors and executive officers is available in its Annual Report on Form 10-K for the 2022 fiscal year and its definitive proxy statement for the 2023 annual meeting of unitholders, each filed with the SEC on February 21, 2023, and the joint proxy statement/prospectus. Other information regarding the participants in the solicitations and a description of their direct and indirect interests, by security holdings or otherwise, are included in the joint proxy statement/prospectus and other relevant materials filed or that may be filed in the future with the SEC regarding the Proposed Transaction when they become available. Shareholders of ONEOK, unitholders of Magellan, potential investors and other readers should read the joint proxy statement/prospectus carefully before making any voting or investment decisions.

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