Notice of Annual Meeting and Proxy Statement Annual Meeting of Shareholders Wednesday, May 23, 2018 Our Values Ethics: Our actions are founded on trust, honesty and integrity through open communications and adherence to the highest standards of personal, professional and business ethics. Quality: Our commitment to quality drives us to make continuous improvements in our quest for excellence. Diversity: We value diversity, as well as the dignity and worth of each employee, and believe that a diverse and inclusive workforce is critical to our continued 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 environment and improving the quality of life for employees where they live and work. Our Strategy ‰ Provide our customers with high quality service through vertical integration across the midstream value chain focused on the trans- portation, fractionation, processing, storage, marketing and delivery of natural gas liquids, natural gas and other hydrocarbon liquid prod- ucts through our strong asset position and experienced team while attracting and retaining a diverse talent base needed to execute our growth strategies ‰ Grow our businessessafely, profitably and in an environmentally sustainable manner while maintaining financial strength ‰ Our focus includes organically growing our franchises and building on our vertically integrated strategy with an emphasis on fee-based earnings. April 5, 2018 Dear Shareholder: You cordially are 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 23, 2018, at ONEOK Plaza, 100 West Fifth Street, Tulsa, Oklahoma 74103. 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 2017 annual report to shareholders alsois enclosed. A report on our 2017 performance will be presented at the meeting. We look forward to greeting as many of our shareholders as possible at the annual meeting. We know, however, that most of our share- holders 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 by a broker, bank, trustee or other similar fiduciary, unless you provide your broker, bank, trustee or other similar fiduciary 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, bank, trustee or other similar fiduciary 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 assoon as possi- ble so that you can be sure your shares will be voted. 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 2018 Annual Meeting of Shareholders Time and date May 23, 2018, at 9:00 a.m. Central Daylight Time Place ONEOK Plaza, 100 WestFifthStreet, Tulsa, Oklahoma 74103 Items of business (1) To consider and vote on the election of the 10 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, 2018. (3) To consider and vote on the ONEOK, Inc. Equity Incentive Plan. (4) To consider and vote on our executive compensation on a non-binding, advisory basis. (5) 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 26, 2018. Only shareholders of record at the closeofbusiness 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 usetheseconvenient voting methods.Ofcourse, 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 proceduressetforthinthe accompanying proxy statement. Whether or not you expect 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 5, 2018. This proxy statement and our 2017 annual report to shareholders areavailableonourwebsite at www.oneok.com. Additionally, you may access this proxy statement and our 2017 annual report at www.proxydocs.com/oke. By order of the Board of Directors, Eric Grimshaw Secretary Tulsa, Oklahoma April 5, 2018 Table of Contents Proxy Statement This proxy statement describes important issues affecting our company and is furnishedinconnectionwiththesolicitation of proxies by our Board of Directors for use at our 2018 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 5, 2018. 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 and references to “ONEOK Partners”orthe “partnership” mean ONEOK Partners,L.P.anditssubsidiaries. SUMMARY PROXY INFORMATION 1 Director Compensation ................................20 Business Highlights ................................... 1 Compensation Committee Interlocks and Insider Participation .........................................22 Corporate Governance Highlights ....................... 3 Executive Sessions of the Board ........................22 Executive Compensation Highlights ...................... 4 Communications with Directors .........................23 Shareholder Actions .................................. 6 Complaint Procedures ................................23 ABOUT THE 2018 ANNUAL MEETING 7 CORPORATE RESPONSIBILITY 24 OUTSTANDING STOCK AND VOTING 11 Safety and Health ....................................24 Matters to Be Voted upon ..............................11 Environment ........................................25 Voting .............................................11 Community Investments ...............................27 Quorum ............................................11 Diversity and Inclusion.................................27 Votes Required ......................................12 Political Advocacy and Oversight ........................28 Revoking a Proxy ....................................12 PROPOSAL 1—Election of Directors 29 Proxy Solicitation .....................................13 Board Refreshment ...................................29 GOVERNANCE OF THE COMPANY 14 Annual Election by Majority Vote .........................29 Corporate Governance Guidelines .......................14 Board Qualifications ..................................29 Code of Business Conduct and Ethics ....................14 Director Nominees ...................................31 Director Independence ................................14 PROPOSAL 2—Ratify the Selection of Board Leadership Structure ............................15 PricewaterhouseCoopers LLP as our Independent Lead Independent Director .............................15 Registered Public Accounting Firm for the Year Ending December 31, 2018 36 Succession Planning ..................................15 Ratification of Selection of PricewaterhouseCoopers LLP as Our Board and Corporate Strategy ......................15 our Independent Registered Public Accounting Firm for Shareholder Engagement ..............................16 2018 ..............................................36 Risk Oversight .......................................16 Audit and Non-Audit Fees ..............................36 Board and Committee Membership......................17 Audit Committee Policy on Services Provided by the Independent Registered