                                                               Exhibit 99 (b)

THIS  DEBENTURE HAS NOT BEEN  REGISTERED  UNDER THE  SECURITIES  ACT OF 1933, AS
AMENDED (THE "ACT"),  OR THE  SECURITIES  LAWS OF ANY STATE AND MAY NOT BE SOLD,
TRANSFERRED,  ASSIGNED OR OTHERWISE DISPOSED OF UNLESS THE PERSON REQUESTING THE
TRANSFER OF THIS  DEBENTURE  SHALL FURNISH,  WITH RESPECT TO SUCH  TRANSFER,  AN
OPINION OF COUNSEL (BOTH COUNSEL AND OPINION TO BE SATISFACTORY TO BOK FINANCIAL
CORPORATION,  HEREIN  CALLED THE  "CORPORATION")  TO THE EFFECT  THAT SUCH SALE,
TRANSFER,  ASSIGNMENT  OR  DISPOSITION  WILL NOT  INVOLVE ANY  VIOLATION  OF THE
REGISTRATION  PROVISIONS OF THE ACT OR ANY SIMILAR OR SUPERSEDING  STATUTE OR OF
ANY APPLICABLE STATE SECURITIES LAW.

THIS  DEBENTURE IS NOT A DEPOSIT AND WILL NOT BE INSURED BY THE FEDERAL  DEPOSIT
INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY. THIS OBLIGATION MAY NOT BE
REPAID PRIOR TO MATURITY, EITHER PURSUANT TO AN ACCELERATION IN EVENT OF DEFAULT
OR OTHERWISE, WITHOUT THE PRIOR WRITTEN CONSENT OF THE ISSUER.

THIS DEBENTURE MAY NOT BE EXCHANGED FOR DEBENTURES OF SMALLER DENOMINATIONS.

                            BOK FINANCIAL CORPORATION
                                  $188,000,000
                                    DEBENTURE

                                  July 21, 2008

BOK FINANCIAL CORPORATION,  hereinafter called the "Corporation",  a corporation
duly organized and existing  under the laws of the State of Oklahoma,  for value
received,  hereby  promises to pay to the order of George B. Kaiser,  the sum of
One Hundred  Eighty-Eight  Million and no/100 Dollars  ($188,000,000) or so much
thereof as shall been  advanced and remains  outstanding  and to pay interest on
the  unpaid  balance  of  such  principal  sum at  the  rate  and in the  manner
hereinafter  provided.  The  Corporation may request  advances,  upon three days
prior notice,  under this  Debenture from time to time provided (i) the total of
all such  advances  of  principal  outstanding  at any  time  shall  not  exceed
$188,000,000  and (ii) the  Corporation  is not in  default  of any  obligations
arising under this Debenture.

The  principal  of and  interest  on this  Debenture  shall  be  payable  at the
principal office of the holder in Tulsa,  Oklahoma,  or at such other address as
the holder of this Debenture shall from time to time designate.

This Debenture is payable as follows:

(a) The unpaid  principal  of this  Debenture  is due and payable on December 2,
2010.

(b) Interest  shall be charged on the unpaid  principal  balance of this Note to
the date of maturity on a daily basis for the actual  number of days any portion
of the principal is outstanding ("Outstanding Principal"), computed on the basis
of a 360 day year, at a rate  determined on the first day of each calendar month
for the entire  calendar  month  equal to (the  "Note  Rate") the LIBOR Rate (as
hereinafter  defined) per annum in effect from time to time.  Interest  shall be
charged on $188,000,000 less the Outstanding  Principal  (calculated and paid in
the  same  manner  as  interest  on the  Outstanding  Principal)  at the rate of
twenty-five  one-hundredths of one percent (0.250%).  "LIBOR Rate" means (i) the
one (1) month London  Interbank  Offered Rate ("LIBOR") as published in the Wall
Street  Journal on the first  business days of each calendar  month (even if the
first  business day occurs after the  beginning of the calendar  month) plus (i)
one hundred  twenty-five  one-hundredths of one percent (1.250%).  The Note Rate
shall be  determined  each month and each  change in the Note Rate shall  become
effective,  without notice to the Maker (which notice is hereby expressly waived
by the Maker) on the effective of such change. The interest on this Debenture is
payable  as it  accrues  on the  last day of each  March,  June,  September  and
December in each year, commencing September 30, 2008, until the principal amount
hereof has been paid in full.

In the event of default  hereunder and this  Debenture is placed in the hands of
an attorney for collection  (whether or not suit is filed), or if this Debenture
is collected by suit or legal proceedings or through bankruptcy proceedings, the
Corporation  agrees to pay in addition  to all sums then due  hereon,  including
principal  and  interest,  all  expenses  of  collection,  including  reasonable
attorneys' fees.

The Corporation  hereby waives  presentment and demand for payment,  protest and
notice of protest and nonpayment  and agrees that  liability  hereunder or under
any  guaranty  of payment  hereof  shall not be affected  by any  renewal(s)  or
extension(s) in time of payment hereof.

All references to the Corporation  herein shall, and shall be deemed to, include
its  successors  and  assigns,  and all  covenants,  stipulations,  promises and
agreements  contained herein by or on behalf of the Corporation shall be binding
upon its successors and assigns, whether so expressed or not.

IN WITNESS WHEREOF,  the Corporation has caused this Debenture to be executed in
its  corporate  name and in its  behalf  by its  Chief  Executive  Officer,  his
signature to be attested by its Secretary and its corporate  seal to be hereunto
affixed and this Debenture to be dated,  issued and  delivered,  all on the 21st
day of July, 2008, each of such officers being thereunto duly authorized.

ATTEST:                                  BOK FINANCIAL CORPORATION

___/s/ Frederic Dorwart_____             By    ______/s/ Stanley A. Lybarger___
Frederic Dorwart, Secretary                    Stanley A. Lybarger,
                                               Chief Executive Officer


                                         George B. Kaiser

                                         _____/s/ George B. Kaiser_____________
