BOK Financial Corporation — pronounced as letters, "B-O-K" — is a financial services holding company headquartered in Tulsa, Oklahoma. Offering a full complement of retail and commercial banking products and services across the American Midwest and Southwest, the company is one of the 50 largest financial services firms in the U.S., and the largest in Oklahoma. The company's banking subsidiary, BOKF, NA, operates under the brands Bank of Oklahoma, Bank of Texas, and Bank of Albuquerque, and it operates as BOK Financial in Arizona, Arkansas, Colorado, Kansas, and Missouri. It also operates ATM and debit card processor TransFund, Cavanal Hill Investment Management, BOK Financial Securities, BOK Financial Advisors, BOK Financial Insurance, and BOK Financial Asset Management. The company is more than 50% owned by George Kaiser, who acquired the bank in 1991 from the FDIC. Known for its energy roots, as of June 30, 2021, 14% of its loan portfolio was to borrowers in the petroleum industry. Wikipedia