EXHIBIT 5.0

Opinion of Frederic Dorwart, Lawyers

August 22, 2002

BOK Financial Corporation
Bank of Oklahoma Tower
Boston Avenue at Second Street
Tulsa, Oklahoma 74172

RE: REGISTRATION STATEMENT ON FORM S-4

Ladies and Gentlemen:

We have examined the Registration Statement on Form S-4 to be filed by you with
the Securities and Exchange Commission in connection with the registration under
the Securities Act of 1933, as amended, of the shares of your common stock to be
offered pursuant to the merger agreement dated May 15, 2002 among BOK Financial
Corporation, Bank of Tanglewood, N.A. and TW Interim National Bank. As your
counsel in connection with these transactions, we have examined the proceedings
taken and proposed to be taken in connection with the issue in sale of the
shares.

It is our opinion that the shares, when issued as described in the Registration
Statement, will be legally and validly issued, fully paid, and non-assessable.

We hereby consent to this opinion being included in the S-4 Registration
Statement of BOK Financial regarding such shares.


                                               FREDERIC DORWART, LAWYERS


                                                  /s/ Frederic Dorwart
                                              ----------------------------------
                                              For the Firm