Important Additional Information and Where to Find It In connection with the proposed merger, BOK Financial has filed with the SEC a Registration Statement on Form S-4 that includes the Proxy Statement of CoBiz Financial Inc. and a Prospectus of BOK Financial. The registration statement, as amended, was declared effective by the SEC on August 16, 2018. CoBiz Financial Inc. commenced the mailing of the definitive Proxy Statement/Prospectus to its shareholders on or about August 20, 2018. INVESTORS AND SHAREHOLDERS ARE URGED TO READ THE PROXY STATEMENT/PROSPECTUS AND OTHER RELEVANT DOCUMENTS FILED OR TO BE FILED WITH THE SEC CAREFULLY WHEN THEY BECOME AVAILABLE BECAUSE THEY CONTAIN AND WILL CONTAIN IMPORTANT INFORMATION. A free copy of the Proxy Statement/Prospectus, as well as other filings containing information about CoBiz Financial Inc. and BOK Financial, may be obtained at the SECs Internet site (http://www.sec.gov). Copies of the Proxy Statement/Prospectus can also be obtained, free of charge, by directing a request to CoBiz Financial Inc. Investor Relations at CoBiz Financial Investor Relations, 1401 Lawrence Street, Suite 1200, Denver, CO, by calling 303.312.3412, or by sending an e-mail to info@cobizfinancial.com or to BOK Financial Investor Relations at Bank of Oklahoma Tower, PO Box 2300, Tulsa, OK, 74192, by calling 918.595.3030 or by sending an e-mail to investorrelations@bokf.com. Information regarding the persons who may, under the rules of the SEC, be considered participants in the solicitation of the shareholders of CoBiz Financial Inc. in connection with the proposed transaction is set forth in the Proxy Statement/Prospectus filed with the SEC. CoBiz Financial Inc. and BOK Financial Corporation and certain of their respective directors and executive officers may be deemed to be participants in the solicitation of proxies from the shareholders of CoBiz Financial Inc. in respect of the transaction described in the Proxy Statement/Prospectus. Information regarding CoBiz Financial Inc.s directors and executive officers is contained in CoBiz Financial Inc.s Annual Report on Form 10-K for the year ended December 31, 2017 and its Proxy Statement on Schedule 14A, dated March 9, 2018, which are filed with the SEC. Additional information regarding the interests of those participants and other persons who may be deemed participants in the transaction may be obtained by reading the Proxy Statement/Prospectus regarding the proposed merger. Free copies of this document may be obtained as described in the preceding paragraph. Forward-Looking Statements This communication contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 including, but not limited to, CoBiz Financial Inc.s and BOK Financial Corporations expectations or predictions of future financial or business performance or conditions. Forward-looking statements are typically identified by words such as believe, expect, anticipate, intend, target, estimate, continue, positions, plan, predict, project, forecast, guidance, goal, objective, prospects, possible or potential, by future conditional verbs such as assume, will, would, should, could or may, or by variations of such words or by similar expressions. These forward-looking statements are subject to numerous assumptions,