BancFirst (BANF) 10-Q 2008 Q1 Quarterly report

Exhibit 32.1

CEO’S CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report on Form 10-Q of BancFirst Corporation (the “Company”) for the period ended March 31, 2008 as filed with the Securities and Exchange Commission (the “Report”), I, David E. Rainbolt, Chief Executive Officer of the Company, certify, pursuant to 18 U.S.C. section 1350, as adopted pursuant to section 906 of the Sarbanes-Oxley Act of 2002, that to the best of my knowledge:

(1) The Report fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/ David E. Rainbolt

David E. Rainbolt

President and Chief Executive Officer

May 9, 2008