BOK Financial Corporation, based in Tulsa, Oklahoma, is a financial services company in the West South Central States region of the United States. The corporate headquarters is located in the BOK Tower in downtown Tulsa. BOK Financial's holdings include BOKF, NA, BOSC, Inc, Cavanal Hill Investment Management and Southwest Trust Company. BOKF, NA operates seven banking divisions: Bank of Albuquerque, Bank of Arizona, Bank of Arkansas, Bank of Kansas City, Bank of Oklahoma, Bank of Texas, and Colorado State Bank and Trust. BOKF, NA has full-service banks located in eight states. BOSC, Inc., the broker/dealer subsidiary, provides brokerage services in 10 states.
 
BOKF has a market value of approximately $3.7 billion USD as June 21, 2011.
 
Corporate history

Foundation
 
BOK traces its roots to the Exchange National Bank of Tulsa, which was formed in 1910 when four men bought the remains of the failed Farmers National Bank. One of the bank's major investors was Harry F. Sinclair, who became the bank's president.
 
In 1917, Exchange National Bank of Tulsa began construction of a headquarters building in Tulsa at Third Street and Boston Avenue. In 1928, the bank constructed a 28-story tower adjacent to the initial building. The combined structure, since renamed the 320 South Boston Building, remained the tallest building in Tulsa until 1967.
 
During the Great Depression, several Tulsa oil men—including William G. Skelly and J.A. Chapman, pumped $18 million of their own wealth into the bank to keep it afloat. As a result, it was a major player in the early 1930s oil boom. In 1933, it was reorganized as the National Bank of Tulsa (NBT).
 
In 1975, NBT changed its name to Bank of Oklahoma (BOK). The following year, BOK began moving its headquarters employees into the new BOK Tower.
 
Expansion
 
Bank of Oklahoma was placed into Federal Deposit Insurance Corporation receivership in 1990, and a year later was bought by Tulsa businessman George Kaiser. At the time, it was a $2 billion bank with 20 branches in Oklahoma.
 
Under Kaiser's ownership, BOK began an aggressive expansion effort. BOK's expansion strategy is to locate in growing markets near Oklahoma. Currently BOK operates banks in 9 states including Oklahoma, New Mexico, Arizona, Arkansas, Texas, Colorado, Kansas, Missouri and Utah. In March 2007, BOK began banking operations in Salt Lake City.  Also in 2007, BOK continued their aggressive push in expanding market share in the Dallas-Fort Worth area. Currently, the Bank of Texas is the 8th largest bank based in Texas with assets of 3.7 billion.
 
On August 17, 2012, BOK Financial acquired Milestone Group. The acquisition is the first since 2007.
 
Sponsorships
 
In 2005, BOK Financial acquired the naming rights for the BOK Center, for a price of $11 million USD.