[4][5] In 1917, Exchange National Bank began construction of a headquarters building in Tulsa at Third Street and Boston Avenue.

[5][8] The following year, the company began moving employees into the new BOK Tower and in 1979, the bank reached $1 billion in assets.

[9][10][11] In 1986, the Federal Deposit Insurance Corp bailed the Bank of Oklahoma out[12] for a total cost of $130 million[9] in a move hailed as an innovative response.

[12] On June 7, 1991, with the company's assets totaling just under $2 billion, it was acquired by George Kaiser, who had served on the bank's board of directors, for $60.7 million in a sale facilitated by the FDIC.

[12][13] Under Kaiser's ownership, the institution became BOK Financial[14] and developed a strategy to locate in growing markets near Oklahoma.