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                                   Exhibit 5.0

                      Opinion of Frederic Dorwart, Lawyers

                                                       
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                                 October 5, 1998
BOK Financial Corporation
One Williams Center
Tulsa, Oklahoma 74172

Ladies and Gentlemen:

         In connection  with the  registration  under the Securities Act of 1933
(the "Act") of  $250,000,000  aggregate  amount of senior debt  securities  (the
"Senior Debt Securities") of BOK Financial Corporation,  an Oklahoma corporation
(the  "Company"),  we, as your counsel,  have examined such  corporate  records,
certificates  and  other  documents,  and  such  questions  of  law,  as we have
considered necessary or appropriate for the purposes of this opinion.

         Upon the basis of such examination,  we advise you that, in our opinion
when the registration  statement  relating to the Securities (the  "Registration
Statement") has become  effective  under the Act, the indenture  relating to the
Senior Debt Securities (the  "Indenture")  has been duly executed and delivered,
the terms of the Senior Debt Securities and of their issuance and sale have been
duly  established  in  conformity  with the  Indenture  so as not to violate any
applicable  law or  result in a default  under or  breach  of any  agreement  or
instrument  binding upon the Company and so as to comply with any requirement or
restriction  imposed by any court or governmental body having  jurisdiction over
the  Company,  and the  Senior  Debt  Securities  have  been duly  executed  and
authenticated   in  accordance  with  the  Indenture  and  issued  and  sold  as
contemplated  in the  Registration  Statement,  the Senior Debt  Securities will
constitute  valid and legally  binding  obligations  of the Company,  subject to
bankruptcy,  insolvency,  fraudulent  transfer,  reorganization,  moratorium and
similar laws of general applicability relating to or affecting creditors' rights
and to general equity principles.

         The  foregoing  opinion is limited  to the  Federal  laws of the United
States, and the laws of the State Oklahoma,  and we are expressing no opinion as
to the effect of the laws of any other jurisdiction.

         We have  relied as to certain  matters  on  information  obtained  from
public officials, officers of the Company and other sources believed by us to be
responsible.

         We hereby  consent to the  filing of this  opinion as an exhibit to the
Registration Statement and to the reference to us under the heading "Validity of
the Senior Debt Securities" in the Prospectus. In giving such consent, we do not
thereby  admit that we are in the category of persons  whose consent is required
under Section 7 of the Act.

                                   Sincerely,


FD/vv                             /s/Frederic Dorwart