Exhibit 8.0
                                                                     -----------

                                August 22, 2002


Bank of Tanglewood, N.A.
500 Chimney Rock Road
Houston, Texas 77056

Ladies and Gentlemen:

We have acted as counsel to Bank of Tanglewood, N.A., a national banking
association organized under the National Bank Act, as amended ("Tanglewood"), in
connection with the merger (the "Merger") of Tanglewood with and into TW Interim
National Bank, an interim national banking association organized under the
National Bank Act ("Merger Sub") and a wholly-owned subsidiary of BOK Financial
Corporation ("BOK Financial"), an Oklahoma corporation and a registered bank
holding company under the Bank Holding Company Act of 1956, as amended, pursuant
to the terms of the Agreement and Plan of Merger dated as of May 15, 2002 (the
"Merger Agreement") by and among Tanglewood, BOK Financial and Merger Sub, each
as described in the Merger Agreement. BOK Financial has filed with the
Securities and Exchange Commission (the "Commission") a registration statement
on Form S-4 with respect to the shares of common stock of BOK Financial, par
value $0.00006 ("BOK Financial Common Stock"), to be issued in connection with
the Merger (the "Registration Statement"), under the Securities Act of 1933, as
amended (the "Securities Act"). This opinion is delivered in accordance with the
terms of the Merger Agreement and the requirements of Item 601(b)(8) of
Regulation S-K under the Securities Act.

In rendering this opinion, we have examined and relied upon the accuracy and
completeness of the facts, information, covenants and representations contained
in originals or copies, certified or otherwise identified to our satisfaction,
of the Merger Agreement and such other documents and records as we have deemed
necessary and relevant for purposes of this opinion. In addition, we have
expressly relied upon certain factual representations made to us by officers of
BOK Financial and Tanglewood. If any statements contained in the Merger
Agreement are not true and accurate, or if any representations made to us are
not true and accurate, then we express no opinion to the extent the subject
matter of this opinion is affected thereby. We have assumed the genuineness of
all signatures, the authenticity of all



Bank of Tanglewood, N.A.
August 22, 2002
Page 2

documents and records submitted to us as originals, the conformity to authentic
original documents and records of all documents and records submitted to us as
copies, and the truthfulness of all statements of fact contained therein. Unless
otherwise defined herein, capitalized terms used herein shall have the meanings
ascribed thereto in the Merger Agreement.

This opinion is based on the current provisions of the Internal Revenue Code of
1986, as amended (the "Code"), Treasury Regulations promulgated thereunder,
pertinent judicial authorities, published pronouncements of the Internal Revenue
Service and such other authorities as we have considered necessary and relevant.
There can be no assurance that the legal authorities upon which this opinion is
based will not be modified, revoked, supplemented, amended, revised, reversed or
overruled. We assume no obligation to update or supplement this opinion to
reflect changes in such legal authorities.

For purposes of this opinion, we have assumed that shares of common stock of
Tanglewood, par value $5.00 per share ("Tanglewood Common Stock"), are held by
Tanglewood shareholders as "capital assets" within the meaning of Section 1221
of the Code. This opinion does not address (i) the tax consequences, if any, to
those Tanglewood shareholders who acquired Tanglewood Common Stock pursuant to
the exercise of compensatory options or warrants or as compensation, (ii) all
aspects of federal income taxation that might be relevant to particular holders
of Tanglewood Common Stock in light of their personal investment circumstances
or (iii) the tax consequences to such holders who are subject to special
treatment under the federal income tax laws, such as foreign persons, dealers in
securities or foreign currencies, regulated investment companies, life insurance
companies, financial institutions, tax-exempt organizations or pass-through
entities. In addition, this opinion does not address the federal income tax
consequences to those who hold Tanglewood Common Stock as part of a "straddle,"
"hedge" or "conversion transaction" as defined in the Code.

In rendering these opinions, we have assumed that the transactions contemplated
by the Merger Agreement and the Registration Statement will be consummated in
accordance with the Merger Agreement.

Based on the foregoing and subject to the limitations and assumptions set forth
herein, and having due regard for such legal considerations as we deem relevant,
we are of the opinion that:



Bank of Tanglewood, N.A.
August 22, 2002
Page 3

1.   The Merger will qualify as a reorganization within the meaning of Section
     368(a)(1)(A) and Section 368(a)(2)(D) of the Code and Tanglewood, BOK
     Financial and Merger Sub will each be a party to the reorganization.

2.   No gain or loss will be recognized by Tanglewood, BOK Financial and Merger
     Sub as a result of the Merger.

3.   No gain or loss will be recognized by Tanglewood shareholders as a result
     of the exchange of Tanglewood Common Stock for BOK Financial Common Stock
     pursuant to the Merger (except for any gain attributable to cash, if any,
     or benchmark price protection rights received pursuant to the terms of the
     Merger Agreement).

4.   Any gain recognized by a Tanglewood shareholder will constitute a long term
     capital gain if such Tanglewood shareholder's holding period in the
     Tanglewood Common Stock exceeds one year at the time of the Merger.

5.   The aggregate tax basis of the BOK Financial Common Stock received by
     Tanglewood shareholders in exchange for their Tanglewood Common Stock will
     be the same as the aggregate tax basis of the shares of the Tanglewood
     Common Stock surrendered in exchange therefor, decreased by the amount of
     the cash, if any, and the fair market value of the benchmark price
     protection rights received in the Merger, and increased by the amount of
     gain recognized as a result of the Merger.

6.   The holding period of the BOK Financial Common Stock to be received by
     Tanglewood shareholders in exchange for their Tanglewood Common Stock will
     include the holding period of the Tanglewood Common Stock surrendered in
     exchange therefor.

Our opinion is limited to the foregoing federal income tax consequences of the
Merger to Tanglewood and Tanglewood shareholders, which are the only matters as
to which you have requested our opinion. We have not addressed any other federal
income tax consequences of the Merger other than those specifically set forth
herein, and we have not considered any matters (including state, local or
foreign tax consequences) arising under the laws of any jurisdiction other than
matters of federal law arising under the laws of the United States as expressly
set forth herein. This opinion is being furnished solely for the benefit of
Tanglewood and Tanglewood shareholders in connection with the closing of the
Merger and may not be used or relied upon by any other party or for any other
purpose. Although this opinion represents our best legal judgment, it has no
binding effect or official status of any kind, and no assurance can be given
that contrary positions will not be taken by the Internal Revenue Service or a
court considering the issues.



Bank of Tanglewood, N.A.
August 22, 2002
Page 4

We hereby consent to the filing of this opinion with the Commission as Exhibit
8.0 to the Registration Statement and to the references to our firm under the
heading "Legal and Tax Matters" in the proxy statement-prospectus included in
the Registration Statement. By giving such consent, we do not admit that we are
experts with respect to any part of the Registration Statement, including this
Exhibit, within the meaning of the term "expert" as used in the Securities Act
or the rules and regulations thereunder.

                                               Very truly yours,
                                               /s/ Bracewell & Patterson, L.L.P.
                                               Bracewell & Patterson, L.L.P.



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