Notice of Annual Meeting and Proxy Statement Annual Meeting of Shareholders Wednesday, May 20, 2020 Our Values Ethics: Our actions are founded on trust, honesty, integrity and respect through open communications and adherence to the highest stan- dards of personal, professional and business ethics. Quality: Our commitment to quality drives us to continuously improve in our quest for excellence. Diversity: We value diversity, the dignity and worth of each employee, and believe that a diverse, inclusive workforce is critical to our con- tinued success. Value: We are committed to creating value for all stakeholders—employees, customers, investors and our communities—through the optimum development and utilization of our resources. Service: We provide responsive, flexible service to customers, and commit to preserving the environment, providing a safe work environ- ment and improving the quality of life for employees where they live and work. Our Core Strategy ‰ Provide our customers with high-quality services through vertical integration across the midstream value chain. ‰ Grow our asset position in a safe, reliable and environmentally sustainable manner. ‰ We achieve this through our strong asset position and experienced team while attracting and retaining the diverse talent base needed to execute our growth strategies. April 3, 2020 Dear Shareholder: You are cordially invited to attend the annual meeting of shareholders of ONEOK, Inc., which will be held at 9:00 a.m. Central Daylight Time on Wednesday, May 20, 2020, at ONEOK Plaza, 100 West Fifth Street, Tulsa, Oklahoma 74103. ANNUAL MEETING The matters to be considered and voted on at the meeting are set forth in the attached notice of the annual meeting and are described in the attached proxy statement. A copy of our 2019 annual report to shareholders is also enclosed. A report on our 2019 performance will be presented at the meeting. VOTING We look forward to greeting as many of our shareholders as possible at the annual meeting. We know, however, that most of our shareholders will be unable to attend. Therefore, proxies are being solicited so that each shareholder has an opportunity to vote by proxy. You can authorize a proxy over the internet or by telephone. Instructions for using these convenient services are included in the proxy statement and on the proxy card. Of course, if you prefer, you may vote by mail by signing, dating and returning the enclosed proxy card in the enclosed postage-paid envelope. If your shares are held through a broker or similar person, unless you provide them with voting instructions, your shares will not be voted in the election of directors or in certain other important proposals as described in the accompanying proxy statement. Consequently, please provide your voting instructions to your broker or similar person in a timely manner to ensure that your shares will be voted. Regardless of the number of shares you own, your vote is important. I urge you to submit your proxy or voting instructions as soon as possible so that you can be sure your shares will be voted. We intend to hold our annual meeting of shareholders in person. However, due to the emerging public health impact of coronavirus disease 2019 (COVID-19), we are planning for the possibility that the annual meeting of shareholders may be held solely by means of a virtual meeting format. If we take this step, we will announce our decision to do so in advance, and details on how to participate will be set forth in a news release issued by us and available at www.oneok.com. Thank you for your investment in ONEOK and your continued support. Very truly yours, John W. Gibson Chairman of the Board ONEOK, Inc. Notice of 2020 Annual Meeting of Shareholders Time and date May 20, 2020, at 9:00 a.m. Central Daylight Time Place ONEOK Plaza, 100 West Fifth Street, Tulsa, Oklahoma 74103 We intend to hold our annual meeting of shareholders in person. However, due to the emerging public health impact of coronavirus disease 2019 (COVID-19), we are planning for the possibility that the annual meeting of shareholders may be held solely by means of a virtual meeting format. If we take this step, we will announce our decision to do so in advance, and details on how to participate will be set forth in a news release issued by us and available at www.oneok.com. Items of business (1) To consider and vote on the election of the 11 director nominees named in the accompanying proxy statement to serve on our Board of Directors. (2) To consider and vote on the ratification of the selection of PricewaterhouseCoopers LLP as the independent registered public accounting firm of ONEOK, Inc., for the year ending December 31, 2020. (3) To consider and vote on our executive compensation on a non-binding, advisory basis. (4) To consider and vote on such other business as may come properly before the meeting or any adjournment or postponement of the meeting. These matters are described more fully in the accompanying proxy statement. Record date March 23, 2020. Only shareholders of record at the close of business on the record date are entitled to receive notice of, and to vote at, the annual meeting. Proxy voting YOUR VOTE IS IMPORTANT The vote of every shareholder is important. The Board of Directors appreciates the cooperation of shareholders in directing proxies to vote at the meeting. To make it easier for you to vote, internet and telephone voting are available. The instructions in the accompanying proxy statement and attached to your proxy card describe how to use these convenient voting methods. Of course, if you prefer, you may vote by mail by completing your proxy card and returning it in the enclosed, postage-paid envelope. You may revoke your proxy at any time by following the procedures set forth in the accompanying proxy statement. Whetherornotyouexpect to attend the meeting in person, we urge you to vote your shares at your earliest convenience. This will ensure the presence of a quorum at the meeting. Voting your shares promptly, via the internet, by telephone, or by signing, dating and returning the enclosed proxy card will save us the expense of additional solicitation. Important Notice Regarding Internet Availability of Proxy Materials. This notice of Annual Meeting and proxy statement and form of proxy are being distributed and made available on or about April 3, 2020. This proxy statement and our 2019 annual report to shareholders are available on our website at www.oneok.com. Additionally, you may access this proxy statement and our 2019 annual report at www.proxydocs.com/oke. By order of the Board of Directors, Eric Grimshaw Secretary Tulsa, Oklahoma April 3, 2020 Table of Contents Proxy Statement This proxy statement describes important issues affecting our company and is furnished in connection with the solicitation of proxies by our Board of Directors for use at our 2020 annual meeting of shareholders to be held at the time and place set forth in the accompanying notice. The approximate date of the mailing of this proxy statement and accompanying proxy card is April 3, 2020. Unless we otherwise indicate or unless the context indicates otherwise, all references in this proxy statement to “ONEOK,” “we,” “our,” “us,” the “company” or similar references mean ONEOK, Inc. and its predecessors and subsidiaries. SUMMARY PROXY INFORMATION 1 Compensation Committee Interlocks and Insider Participation .........................................22 Business Highlights ................................... 1 Executive Sessions of the Board ........................22 Corporate Governance Highlights ....................... 3 Annual Board and Committee Evaluations .................22 Executive Compensation Highlights ...................... 3 Communications with Directors .........................22 Shareholder Actions .................................. 6 Complaint Procedures ................................23 ABOUT THE 2020 ANNUAL MEETING 7 CORPORATE SUSTAINABILITY 24 OUTSTANDING STOCK AND VOTING 11 Environment, Safety and Health Commitment ..............25 Matters to Be Voted upon ..............................11 Safety and Health ....................................26 Voting .............................................11 Human Capital Management ...........................28 Quorum ............................................11 Community Investments ...............................29 Votes Required ......................................12 Political Advocacy and Oversight ........................29 Revoking a Proxy ....................................12 Proxy Solicitation .....................................12 PROPOSAL1—Election of Directors 31 Board Refreshment ...................................31 GOVERNANCE OF THE COMPANY 13 Annual Election by Majority Vote .........................31 Corporate Governance Guidelines .......................13 Board Qualifications ..................................31 Code of Business Conduct and Ethics ....................13 Summary of Director Qualifications and Experience .........32 Director Independence ................................13 Board Tenure .......................................33 Board Leadership Structure ............................14 Board Diversity ......................................33 Lead Independent Director .............................14 Director Nominees ...................................34 CEO and Senior Management Succession Planning .........14 Our Board and Corporate Strategy ......................14 PROPOSAL2—Ratify the Selection of Shareholder