EXHIBIT 5

                      McCutchen Doyle Brown & Enersen LLP
                            Three Embarcadero Center
                            San Francisco, CA 94111

                                                          Direct: (415) 393-2188
                                                                 treddy@mdbe.com

                                                                  April 12, 2002

Westamerica Bancorporation
1108 Fifth Avenue
San Rafael, California 94901

     REGISTRATION STATEMENT ON FORM S-4

Ladies and Gentlemen:

     We have acted as counsel for Westamerica Bancorporation, a California
corporation (the "Company"), in connection with the Registration Statement on
Form S-4 filed by the Company under the Securities Act of 1933, as amended,
relating to the registration of up to 420,000 shares of Common Stock, no par
value, of the Company to be issued to shareholders of common stock of Kerman
State Bank in accordance with that certain Agreement and Plan of Reorganization
dated as of February 25, 2002, among the Company, Westamerica Bank and Kerman
State Bank.

     We are of the opinion that the foregoing securities have been duly
authorized and, when sold pursuant to the terms described in the Registration
Statement, will be duly and validly issued, fully paid and nonassessable.

     We hereby consent to the filing of this opinion as Exhibit 5 to the
Registration Statement and to the use of our name under the caption "Legal
Matters" in the Registration Statement and in the proxy statement/prospectus
included therein.

                                          Very truly yours,

                                          /s/ MCCUTCHEN, DOYLE, BROWN & ENERSEN,
                                                          LLP

                                          By       /s/ THOMAS G. REDDY
                                            ------------------------------------
                                                    A Member of the Firm