Exhibit 11 WESTAMERICA BANCORPORATION Computation of Earnings Per Share on Common and Common Equivalent Shares and on Common Shares Assuming Full Dilution - ------------------------------------------------------------------------------------------ For the three For the nine months ended months ended September 30, September 30, (In thousands, except per share data) 1999 1998 1999 1998 - ------------------------------------------------------------------------------------------ Weighted average number of common shares outstanding - basic 38,266 41,600 38,976 42,312 Add exercise of options reduced by the number of shares that could have been purchased with the proceeds of such exercise 606 665 625 736 - ------------------------------------------------------------------------------------------ Weighted average number of common shares outstanding - diluted 38,872 42,265 39,601 43,048 ========================================================================================== Net income $19,289 $18,436 $56,562 $54,634 Basic earnings per share $0.50 $0.44 $1.45 $1.29 Diluted earnings per share $0.50 $0.44 $1.43 $1.27