Westamerica Bancorporation (WABC) 10-Q 2010 Q3 Quarterly report

EXHIBIT 32.2

CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350 AS ADOPTED PURSUANT TOSECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report of Westamerica Bancorporation (the Company) on Form 10-Q for the period ended September 30, 2010 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, John “Robert” Thorson, Chief Financial 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:

(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/ John “Robert” ThorsonJohn “Robert” Thorson

Senior Vice President and Chief Financial Officer

Date: October 29, 2010