UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-K

Commission file number: 001-9383

Westamerica Bancorporation

(Exact name of the registrant as specified in its charter)

1108 Fifth Avenue, San Rafael, California 94901

(Address of principal executive offices and zip code)

Registrant’s telephone number, including area code:

(707) 863-6000

Securities registered pursuant to Section 12(b) of the Act:

None

Securities registered pursuant to Section 12(g) of the Act:

Title of Class: Common Stock, no par value

      Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.     Yes þ          No o

      Indicate by check mark if disclosure of delinquent filers pursuant to item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of the registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.     o

      Indicate by check mark whether the registrant is an accelerated filer (as defined in Rule 12b-2 of the Act).     Yes þ          No o

      The aggregate market value of the Common Stock held by non-affiliates of the registrant as of June 30, 2004 as reported on the Nasdaq National Market System, was approximately $1,598,661,045.43. Shares of Common Stock held by each officer and director and by each person who owns 5% or more of the outstanding Common Stock have been excluded in that such persons may be deemed to be affiliates. This determination of affiliate status is not necessarily a conclusive determination for other purposes.

      Number of shares outstanding of each of the registrant’s classes of common stock, as of the close of business on March 8, 2005: 33,009,928 Shares

DOCUMENTS INCORPORATED BY REFERENCE

      Portions of the definitive Proxy Statement relating to registrant’s Annual Meeting of Stockholders, to be held on April 28, 2005, are incorporated by reference in Items 10, 11, 12, 13 and 14 of Part III to the extent described therein.

TABLE OF CONTENTS

FORWARD-LOOKING STATEMENTS

      This Annual Report on Form 10-K contains forward-looking statements about Westamerica Bancorporation for which it claims the protection of the safe harbor provisions contained in the Private Securities Litigation Reform Act of 1995. These forward-looking statements are based on Management’s current knowledge and belief and include information concerning the Company’s possible or assumed future financial condition and results of operations. A number of factors, some of which are beyond the Company’s ability to predict or control, could cause future results to differ materially from those contemplated. These factors include but are not limited to (1) a slowdown in the national and California economies; (2) economic uncertainty created by terrorist threats and attacks on the United States and the actions taken in response; (3) the prospect of additional terrorist attacks in the United States and the uncertain effect of these events on the national and regional economies; (4) changes in the interest rate environment; (5) changes in the regulatory environment; (6) increasing competitive pressure in the banking industry; (7) operational risks including data processing system failures or fraud; (8) the effect of acquisitions and integration of acquired businesses; (9) volatility of rate sensitive deposits; (10) asset/liability matching risks and liquidity risks; and (11) changes in the securities markets. See also “Certain Additional Business Risks” in Item 1. and other risk factors discussed elsewhere in this Report.

PART I

      WESTAMERICA BANCORPORATION (the “Company”) is a bank holding company registered under the Bank Holding Company Act of 1956, as amended (“BHC”). Its legal headquarters are located at 1108 Fifth Avenue, San Rafael, California 94901. Principal administrative offices are located at 4550 Mangels Boulevard in Fairfield, California 94534 and its telephone number is (707) 863-6000. The Company provides a full range of banking services to individual and corporate customers in Northern and Central California through its subsidiary bank, Westamerica Bank (“WAB” or the “Bank”). The principal communities served are Nevada Counties in the North to Kern County in the South. The Company’s strategic focus is on the banking needs of small businesses. In addition, the Company also owns 100% of the capital stock of Community Banker Services Corporation, a company engaged in providing the Company and its subsidiaries data processing services and other support functions.

      The Company was incorporated under the laws of the State of California in 1972 as “Independent Bankshares Corporation” pursuant to a plan of reorganization among three previously unaffiliated Northern California banks. The Company operated as a multi-bank holding company until mid-1983, at which time the then six subsidiary banks were merged into a single bank named Westamerica Bank and the name of the holding company was changed to Westamerica Bancorporation.

      The Company acquired five additional banks within its immediate market area during the early to mid 1990’s. In April, 1997, the Company acquired ValliCorp Holdings, Inc., parent company of ValliWide Bank, the largest independent bank holding company headquartered in Central California. Under the terms of all of the merger agreements, the Company issued shares of its common stock in exchange for all of the outstanding shares of the acquired institutions. The subsidiary banks acquired were merged with and into WAB. These business combinations were accounted for as poolings-of-interests.

      In August, 2000, the Company acquired First Counties Bank. The acquisition was valued at approximately $19.7 million and was accounted for using the purchase accounting method. The assets and liabilities of First Counties Bank were fully merged into WAB in September 2000. First Counties Bank had $91 million in assets and offices in Lake, Napa, and Colusa counties.

      In June of 2002 the Company acquired Kerman State Bank. The acquisition was valued at approximately $14.6 million and was accounted for using the purchase accounting method. The assets and liabilities of Kerman State Bank were fully merged into WAB immediately upon consummation of the merger. Kerman State Bank had $95 million in assets and three offices in Fresno county.

      On March 1, 2005, the Company acquired Santa Rosa based Redwood Empire Bancorp, the parent company of National Bank of the Redwoods (NBR). Based on the Company’s closing stock price on March 1, 2005, the cash and stock consideration, including the value of converted stock options and certain transaction costs, paid in the acquisition was valued at approximately $153 million. As of December 31, 2004, Redwood Empire had $511 million in assets and National Bank of the Redwoods had $436 million in loans and $391 million in deposits at seven banking offices located in Sonoma (5), Lake (1) and Mendocino (1) counties.

      As of the close of business on March 11, 2005, NBR was merged with and into Westamerica Bank. Three former NBR branches were consolidated into existing nearby Westamerica Bank branches and a fourth is expected to be consolidated during the second quarter of 2005. Westamerica has entered into an agreement to sell the former NBR branch in Lake County. This transaction is expected to be consummated during the summer of 2005. Two other branches located in Sonoma County will continue as Westamerica branches.

      At December 31, 2004, the Company had consolidated assets of approximately $4.7 billion, deposits of approximately $3.6 billion and shareholders’ equity of approximately $358.6 million. The Company and its subsidiaries employed 957 full-time equivalent staff.

      The Company makes available free of charge its annual report on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K and any amendments to those reports as well as beneficial ownership reports on Forms 3, 4 and 5 as soon as reasonably practicable after they are electronically filed with or furnished to the Securities and Exchange Commission (“SEC”) through its website (http://www.westamerica.com). Such documents are also available through the SEC’s website (http://www.sec.gov). Requests for the Form 10-K annual report, as well as the Company’s employee Code of Conduct and Ethics, can also be submitted to:

Certain Additional Business Risks

      The Company’s business, financial condition and operating results can be impacted by a number of factors including, but not limited to, those set forth below, any one of which could cause the Company’s actual results to vary materially from recent results or from the Company’s anticipated future results.

      A portion of the loan portfolio of the Company is dependent on real estate. At December 31, 2004, real estate served as the principal source of collateral with respect to approximately 50% of the Company’s loan portfolio. A worsening of current economic conditions, increased economic uncertainty created by concerns regarding terrorist attacks and geo-political risks, or rising interest rates could have an adverse effect on the demand for new loans, the ability of borrowers to repay outstanding loans, the value of real estate and other collateral securing loans and the value of the available for sale securities portfolio, as well as the Company’s financial condition and results of operations in general and the market value of the Company’s common stock. Acts of nature, including earthquakes and floods, which may cause uninsured damage and other loss of value to real estate that secures these loans, may also negatively impact the Company’s financial condition and results of operations.

      The earnings and growth of the Company are affected not only by local market area factors and general economic conditions, but also by government monetary and fiscal policies. Such policies influence the growth of loans, investments and deposits and also affect interest rates charged on loans and paid on deposits. The nature and impact of future changes in such policies on the business and earnings of the Company cannot be predicted. Additionally, state and federal tax policies can impact banking organizations.

      As a consequence of the extensive regulation of commercial banking activities in the United States, the business of the Company is particularly susceptible to being affected by the enactment of federal and state legislation which may have the effect of increasing or decreasing the cost of doing business, modifying permissible activities or enhancing the competitive position of other financial institutions. Any change in applicable laws or regulations may have a material adverse effect on the business and prospects of the Company.

      The Company is also subject to certain operations risks, including, but not limited to, data processing system failures and errors and customer or employee fraud. The Company maintains a system of internal controls and procedures to mitigate against such occurrences and maintains insurance coverage for certain of such risks, but should such an event occur that is not prevented or detected by the Company’s internal controls, is not insured or is in excess of applicable insurance limits, it could have an adverse impact on the Company’s business, financial condition or results of operations.

      Shares of Company common stock eligible for future sale could have a dilutive effect on the market for Company common stock and could adversely affect the market price. The Articles of Incorporation of the Company authorize the issuance of 150 million shares of common stock (and two additional classes of 1 million shares each, denominated “Class B Common Stock” and “Preferred Stock”, respectively) of which approximately 31.6 million were outstanding at December 31, 2004. Pursuant to its stock option plans, at December 31, 2004, the Company had exercisable options outstanding of 2.0 million. As of December 31,

2004, 7.1 million shares of Company common stock remained available for grants under the Company’s stock option plans (and stock purchase plan). Sales of substantial amounts of Company common stock in the public market could adversely affect the market price of its common stock.

      The following is not intended to be an exhaustive description of the statutes and regulations applicable to the Company’s or the Bank’s business. The description of statutory and regulatory provisions is qualified in its entirety by reference to the particular statutory or regulatory provisions. Moreover, major new legislation and other regulatory changes affecting the Company, the Bank, banking, and the financial services industry in general have occurred in the last several years and can be expected to occur in the future. The nature, timing and impact of new and amended laws and regulations cannot be accurately predicted.

      The Company is a bank holding company subject to the Bank Holding Company Act of 1956, as amended (the “BHCA”). The Company reports to, is registered with, and may be examined by, the Board of Governors of the Federal Reserve System (“FRB”). The FRB also has the authority to examine the Company’s subsidiaries. The costs of any examination by the FRB are payable by the Company. The Company is a bank holding company within the meaning of Section 3700 of the California Financial Code. As such, the Company and the Bank are subject to examination by, and may be required to file reports with, the California Commissioner of Financial Institutions (the “Commissioner”).

      The FRB has significant supervisory and regulatory authority over the Company and its affiliates. The FRB requires the Company to maintain certain levels of capital. See “Capital Standards.” The FRB also has the authority to take enforcement action against any bank holding company that commits any unsafe or unsound practice, or violates certain laws, regulations or conditions imposed in writing by the FRB. Under the BHCA, the Company is required to obtain the prior approval of the FRB before it acquires, merges or consolidates with any bank or bank holding company. Any company seeking to acquire, merge or consolidate with the Company also would be required to obtain the prior approval of the FRB.

      The Company is generally prohibited under the BHCA from acquiring ownership or control of more than 5% of any class of voting shares of any company that is not a bank or bank holding company and from engaging directly or indirectly in activities other than banking, managing banks, or providing services to affiliates of the holding company. However, a bank holding company, with the approval of the FRB, may engage, or acquire the voting shares of companies engaged, in activities that the FRB has determined to be closely related to banking or managing or controlling banks. A bank holding company must demonstrate that the benefits to the public of the proposed activity will outweigh the possible adverse effects associated with such activity.

      The FRB generally prohibits a bank holding company from declaring or paying a cash dividend that would impose undue pressure on the capital of subsidiary banks or would be funded only through borrowing or other arrangements which might adversely affect a bank holding company’s financial position. Under the FRB policy, a bank holding company should not continue its existing rate of cash dividends on its common stock unless its net income is sufficient to fully fund each dividend and its prospective rate of earnings retention appears consistent with its capital needs, asset quality and overall financial condition. See the section entitled “Restrictions on Dividends and Other Distributions” for additional restrictions on the ability of the Company and the Bank to pay dividends.

      Transactions between the Company and the Bank are restricted under Regulation W, which became effective on April 1, 2003. The regulation codifies prior interpretations of the FRB and its staff under Sections 23A and 23B of the Federal Reserve Act. In general, subject to certain specified exemptions, a bank or its subsidiaries are limited in their ability to engage in “covered transactions” with affiliates: (a) to an amount equal to 10% of the bank’s capital and surplus, in the case of covered transactions with any one affiliate; and (b) to an amount equal to 20% of the bank’s capital and surplus, in the case of covered transactions with all affiliates. The Company is considered to be an affiliate of the Bank.

      A “covered transaction” includes, among other things, a loan or extension of credit to an affiliate; a purchase of securities issued by an affiliate; a purchase of assets from an affiliate, with some exceptions; and the issuance of a guarantee, acceptance or letter of credit on behalf of an affiliate.

      Federal regulations governing bank holding companies and change in bank control (Regulation Y) provide for a streamlined and expedited review process for bank acquisition proposals submitted by well-run bank holding companies. These provisions of Regulation Y are subject to numerous qualifications, limitations and restrictions. In order for a bank holding company to qualify as “well-run,” both it and the insured depository institutions which it controls must meet the “well capitalized” and “well managed” criteria set forth in Regulation Y.

      On March 11, 2000, the Gramm-Leach-Bliley Act (the “GLBA”), or the Financial Services Act of 1999 became effective. The GLBA repealed provisions of the Glass-Steagall Act, which had prohibited commercial banks and securities firms from affiliating with each other and engaging in each other’s businesses. Thus, many of the barriers prohibiting affiliations between commercial banks and securities firms have been eliminated.

      The BHCA was also amended by the GLBA to allow new “financial holding companies” (“FHCs”) to offer banking, insurance, securities and other financial products to consumers. Specifically, the GLBA amended section 4 of the BHCA in order to provide for a framework for the engagement in new financial activities. A bank holding company (“BHC”) may elect to become a FHC if all its subsidiary depository institutions are well capitalized and well managed. If these requirements are met, a BHC may file a certification to that effect with the FRB and declare that it elects to become a FHC. After the certification and declaration is filed, the FHC may engage either de novo or though an acquisition in any activity that has been determined by the FRB to be financial in nature or incidental to such financial activity. BHCs may engage in financial activities without prior notice to the FRB if those activities qualify under the new list of permissible activities in section 4(k) of the BHCA. However, notice must be given to the FRB within 30 days after a FHC has commenced one or more of the financial activities. The Company has not elected to become a FHC.

      Under the GLBA, Federal Reserve member banks, subject to various requirements, as well as national banks, are permitted to engage through “financial subsidiaries” in certain financial activities permissible for affiliates of FHCs. However, to be able to engage in such activities the Bank must also be well capitalized and well managed and have received at least a “satisfactory” rating in its most recent CRA examination. The Company cannot be certain of the effect of the foregoing recently enacted legislation on its business, although there is likely to be consolidation among financial services institutions and increased competition for the Company.

      The Bank is a California state-chartered bank, is insured by the Federal Deposit Insurance Corporation (the “FDIC”) and is a member bank of the Federal Reserve System. As such, the Bank is subject to regulation, supervision and regular examination by the California Department of Financial Institutions (“DFI”) and the FRB. As a member bank of the Federal Reserve System, the Bank’s primary federal regulator is the FRB. The regulations of these agencies affect most aspects of the Bank’s business and prescribe permissible types of loans and investments, the amount of required reserves, requirements for branch offices, the permissible scope of its activities and various other requirements.

      In addition to federal banking law, the Bank is also subject to applicable provisions of California law. Under California law, the Bank is subject to various restrictions on, and requirements regarding, its operations and administration including the maintenance of branch offices and automated teller machines, capital requirements, deposits and borrowings, stockholder rights and duties, and investment and lending activities.

      California law permits a state chartered bank to invest in the stock and securities of other corporations, subject to a state-chartered bank receiving either general authorization or, depending on the amount of the proposed investment, specific authorization from the Commissioner. However, because the Bank is a member of the Federal Reserve System, its investment authority is limited by regulations promulgated by the FRB. In addition, the Federal Deposit Insurance Corporation Improvement Act (“FDICIA”) imposes limitations on

the activities and equity investments of state chartered, federally insured banks. FDICIA also prohibits a state bank from making an investment or engaging in any activity as a principal that is not permissible for a national bank, unless the Bank is adequately capitalized and the FDIC approves the investment or activity after determining that such investment or activity does not pose a significant risk to the deposit insurance fund.

      The federal banking agencies have risk-based capital adequacy guidelines intended to provide a measure of capital adequacy that reflects the degree of risk associated with a banking organization’s operations for both transactions reported on the balance sheet as assets, and transactions such as letters of credit and recourse arrangements, which are recorded as off balance sheet items. Under these guidelines, nominal dollar amounts of assets and credit equivalent amounts of off balance sheet items are multiplied by one of several risk adjustment percentages, which range from 0% for assets with low credit risk, such as certain U.S. government securities, to 100% for assets with relatively higher credit risk, such as certain loans.

      A banking organization’s risk-based capital ratios are obtained by dividing its qualifying capital by its total risk-adjusted assets and off balance sheet items.

      The federal banking agencies take into consideration concentrations of credit risk and risks from nontraditional activities, as well as an institution’s ability to manage those risks, when determining the adequacy of an institution’s capital. This evaluation is made as a part of the institution’s regular safety and soundness examination. The federal banking agencies also consider interest rate risk (when the interest rate sensitivity of an institution’s assets does not match the sensitivity of its liabilities or its off balance sheet position) in evaluation of a bank’s capital adequacy.

      As of December 31, 2004, the Company’s and the Bank’s respective ratios exceeded applicable regulatory requirements. See Note 8 to the consolidated financial statements for capital ratios of the Company and the Bank, compared to the standards for well capitalized depository institutions and for minimum capital requirements.

      FDICIA requires each federal banking agency to take prompt corrective action to resolve the problems of insured depository institutions, including but not limited to those that fall below one or more prescribed minimum capital ratios.

      An institution that, based upon its capital levels, is classified as “well capitalized,” “adequately capitalized” or “undercapitalized” may be treated as though it were in the next lower capital category if the appropriate federal banking agency, after notice and opportunity for hearing, determines that an unsafe or unsound condition or an unsafe or unsound practice warrants such treatment. At each successive lower capital category, an insured depository institution is subject to more restrictions. In addition to measures taken under the prompt corrective action provisions, commercial banking organizations may be subject to potential enforcement actions by the federal banking agencies for unsafe or unsound practices in conducting their businesses or for violations of any law, rule, regulation or any condition imposed in writing by the agency or any written agreement with the agency.

      FDICIA also implemented certain specific restrictions on transactions and required federal banking regulators to adopt overall safety and soundness standards for depository institutions related to internal control, loan underwriting and documentation and asset growth. Among other things, FDICIA limits the interest rates paid on deposits by undercapitalized institutions, restricts the use of brokered deposits, limits the aggregate extensions of credit by a depository institution to an executive officer, director, principal shareholder or related interest, and reduces deposit insurance coverage for deposits offered by undercapitalized institutions for deposits by certain employee benefits accounts. The federal banking agencies may require an institution to submit to an acceptable compliance plan as well as have the flexibility to pursue other more appropriate or

effective courses of action given the specific circumstances and severity of an institution’s noncompliance with one or more standards.

      Federal banking agencies require banks to maintain adequate valuation allowances for potential credit losses. The Company has an internal staff that continually reviews loan quality and ultimately reports to the Board of Directors. This analysis includes a detailed review of the classification and categorization of problem loans, assessment of the overall quality and collectibility of the loan portfolio, consideration of loan loss experience, trends in problem loans, concentration of credit risk, and current economic conditions, particularly in the Bank’s market areas. Based on this analysis, management, with the review and approval of the Board, determines the adequate level of allowance required. The allowance is allocated to different segments of the loan portfolio, but the entire allowance is available for the loan portfolio in its entirety.

      The power of the board of directors of an insured depository institution to declare a cash dividend or other distribution with respect to capital is subject to statutory and regulatory restrictions which limit the amount available for such distribution depending upon the earnings, financial condition and cash needs of the institution, as well as general business conditions. FDICIA prohibits insured depository institutions from paying management fees to any controlling persons or, with certain limited exceptions, making capital distributions, including dividends, if, after such transaction, the institution would be undercapitalized.

      In addition to the restrictions imposed under federal law, banks chartered under California law generally may only pay cash dividends to the extent such payments do not exceed the lesser of retained earnings of the bank or the bank’s net income for its last three fiscal years (less any distributions to shareholders during this period). In the event a bank desires to pay cash dividends in excess of such amount, the bank may pay a cash dividend with the prior approval of the Commissioner in an amount not exceeding the greatest of the bank’s retained earnings, the bank’s net income for its last fiscal year or the bank’s net income for its current fiscal year.

      The federal banking agencies also have the authority to prohibit a depository institution from engaging in business practices which are considered to be unsafe or unsound, possibly including payment of dividends or other payments under certain circumstances even if such payments are not expressly prohibited by statute.

      The Bank’s deposits are insured by the Bank Insurance Fund (BIF) administered by the FDIC. FDICIA established several mechanisms to increase funds to protect deposits insured by the BIF administered by the FDIC. The FDIC is authorized to borrow up to $30 billion from the United States Treasury; up to 90% of the fair market value of assets of institutions acquired by the FDIC as receiver from the Federal Financing Bank; and from depository institutions which are members of the BIF. Any borrowings not repaid by asset sales are to be repaid through insurance premiums assessed to member institutions. Such premiums must be sufficient to repay any borrowed funds within 15 years and provide insurance fund reserves of $1.25 for each $100 of insured deposits. FDICIA also provides authority for special assessments against insured deposits. No assurance can be given at this time as to what the future level of insurance premiums will be.

      The Bank is subject to certain fair lending requirements and reporting obligations involving home mortgage lending operations and Community Reinvestment Act (“CRA”) activities. The CRA generally requires the federal banking agencies to evaluate the record of a financial institution in meeting the credit needs of their local communities, including low and moderate income neighborhoods. In addition to substantive penalties and corrective measures that may be required for a violation of certain fair lending laws, the federal banking agencies may take compliance with such laws and CRA into account when regulating and supervising other activities.

      The GLBA, in addition to the previously described changes in permissible nonbanking activities permitted to banks, BHCs and FHCs, also required the federal banking agencies, among other federal regulatory agencies, to adopt regulations governing the privacy of consumer financial information. The FRB adopted such regulations with an effective date of November 13, 2000, and a date of full compliance with the regulations on July 1, 2001. The Bank is subject to the FRB’s regulations.

      The federal bank regulatory agencies have established standards for safeguarding nonpublic personal information about customers that implement provisions of the GLBA (the “Guidelines”). Among other things, the Guidelines require each financial institution, under the supervision and ongoing oversight of its Board of Directors or an appropriate committee thereof, to develop, implement and maintain a comprehensive written information security program designed to ensure the security and confidentiality of customer information, to protect against any anticipated threats or hazards to the security or integrity of such information, and to protect against unauthorized access to or use of such information that could result in substantial harm or inconvenience to any customer.

      On October 26, 2001, the President signed into law the Uniting and Strengthening America by Providing Appropriate Tools Required to Intercept and Obstruct Terrorism Act of 2001 or the “USA Patriot Act.” Title III of the Act is the International Money Laundering Abatement and Anti-Terrorist Financing Act of 2001. It includes numerous provisions for fighting international money laundering and blocking terrorist access to the U.S. financial system. The goal of Title III is to prevent the U.S. financial system and the U.S. clearing mechanisms from being used by parties suspected of terrorism, terrorist financing and money laundering.

      The provisions of Title III of the USA Patriot Act which affect banking organizations, including the Bank, are generally set forth as amendments to the Bank Secrecy Act. These provisions relate principally to U.S. banking organizations’ relationships with foreign banks and with persons who are resident outside the United States. The USA Patriot Act does not immediately impose any new filing or reporting obligations for banking organizations, but does require certain additional due diligence and recordkeeping practices. Some requirements take effect without the issuance of regulations. Other provisions were implemented through regulations promulgated by the U.S. Department of the Treasury, in consultation with the FRB and other federal financial institutions regulators.

      On July 30, 2002, the U.S. Congress enacted the Sarbanes-Oxley Act of 2002 (“Sarbanes-Oxley”). The stated goals of Sarbanes-Oxley are to increase corporate responsibility, to provide for enhanced penalties for accounting and auditing improprieties at publicly traded companies and to protect investors by improving the accuracy and reliability of corporate disclosures pursuant to the securities laws. Sarbanes-Oxley generally applies to all companies, both U.S. and non-U.S., that file or are required to file periodic reports under the Securities Exchange Act of 1934 (the “Exchange Act”).

      Sarbanes-Oxley includes very specific additional disclosure requirements and new corporate governance rules, requires the SEC and securities exchanges to adopt extensive additional disclosure, corporate governance and other related rules and mandates further studies of certain issues. Sarbanes-Oxley represents significant federal involvement in matters traditionally left to state regulatory systems, such as the regulation of the accounting profession, and to state corporate law, such as the relationship between a board of directors and management and between a board of directors and its committees and public company shareholders.

      Sarbanes-Oxley addresses, among other matters: (i) independent audit committees for reporting companies whose securities are listed on national exchanges or automated quotation systems (the “Exchanges”) and expanded duties and responsibilities for audit committees; (ii) certification of financial statements by the chief executive officer and the chief financial officer; (iii) the forfeiture of bonuses or other incentive-based compensation and profits from the sale of an issuer’s securities by directors and senior officers

in the twelve month period following initial publication of any financial statements that later require restatement; (iv) a prohibition on insider trading during pension plan black out periods; (v) disclosure of off-balance sheet transactions; (vi) a prohibition on personal loans to directors and officers under most circumstances; (vii) expedited electronic filing requirements related to trading by insiders in an issuer’s securities on Form 4; (viii) disclosure of a code of ethics and filing a Form 8-K for a change or waiver of such code; (ix) accelerated filing of periodic reports; (x) the formation of the Public Company Accounting Oversight Board (“PCAOB”) to oversee public accounting firms and the audit of public companies that are subject to the securities laws; (xi) auditor independence; (xii) internal control evaluation and reporting; and (xiii) various increased criminal penalties for violations of securities laws.

      Given the extensive role of the SEC, the PCAOB and the Exchanges in implementing rules relating to Sarbanes-Oxley’s new requirements, the federalization of certain elements traditionally within the sphere of state corporate law, the impact of Sarbanes-Oxley on reporting companies have been and will continue to be significant.

      Changes to state laws and regulations (including changes in interpretation or enforcement) can affect the operating environment of bank holding companies and their subsidiaries in substantial and unpredictable ways. From time to time, various legislative and regulatory proposals are introduced. These proposals, if codified, may change banking statutes and regulations and the Company’s operating environment in substantial and unpredictable ways. If codified, these proposals could increase or decrease the cost of doing business, limit or expand permissible activities or affect the competitive balance among banks, savings associations, credit unions and other financial institutions. The Company cannot accurately predict whether those changes in laws and regulations will occur, and, if those changes occur, the ultimate effect they would have upon our financial condition or results of operations. It is likely, however, that the current high level of enforcement and compliance-related activities of federal and state authorities will continue and potentially increase.

Competition

      In the past, WAB’s principal competitors for deposits and loans have been other banks (particularly major banks), savings and loan associations and credit unions. To a lesser extent, competition was also provided by thrift and loans, mortgage brokerage companies and insurance companies. Other institutions, such as brokerage houses, mutual fund companies, credit card companies, and certain retail establishments have offered investment vehicles which also compete with banks for deposit business. Federal legislation in recent years has encouraged competition between different types of financial institutions and fostered new entrants into the financial services market, and it is anticipated that this trend will continue.

      The enactment of the Interstate Banking and Branching Act in 1994 and the California Interstate Banking and Branching Act of 1995 have increased competition within California. Regulatory reform, as well as other changes in federal and California law will also affect competition. While the impact of these changes, and of other proposed changes, cannot be predicted with certainty, it is clear that the business of banking in California will remain highly competitive.

      Legislative changes, as well as technological and economic factors, can be expected to have an ongoing impact on competitive conditions within the financial services industry. As an active participant in the financial markets, the Company believes that it continually adapts to these changing competitive conditions.

     Branch Offices and Facilities

      WAB is engaged in the banking business through 87 offices in 22 counties in Northern and Central California including thirteen offices in Fresno County, eleven in Marin County, nine in Sonoma County, seven in Napa County, six in Kern County, five each in Stanislaus, Lake, Contra Costa and Solano Counties, three each in Alameda and Sacramento Counties, two each in Mendocino, Nevada, Placer and Tulare Counties, and one each in Colusa, Merced, San Francisco, Tuolumne, Kings, Madera, and Yolo Counties. WAB believes all of its offices are constructed and equipped to meet prescribed security requirements.

      The Company owns 29 branch office locations and one administrative facility and leases 66 facilities. Most of the leases contain multiple renewal options and provisions for rental increases, principally for changes in the cost of living index, property taxes and maintenance.

      Neither the Company nor any of its subsidiaries is a party to any material pending legal proceeding, nor is their property the subject of any material pending legal proceeding, except ordinary routine legal proceedings arising in the ordinary course of the Company’s business. None of these proceedings is expected to have a material adverse impact upon the Company’s business, financial position or results of operations.

      There were no matters submitted to a vote of the shareholders during the fourth quarter of 2004.

PART II

      The Company’s common stock is traded on the NASDAQ National Market System (“NASDAQ”) under the symbol “WABC”. The following table shows the high and the low bid prices for the common stock, for each quarter, as reported by NASDAQ:

      As of February 28, 2005, there were approximately 8,600 shareholders of record of the Company’s common stock.

      The Company has paid cash dividends on its common stock in every quarter since its formation in 1972, and it is currently the intention of the Board of Directors of the Company to continue payment of cash dividends on a quarterly basis. There is no assurance, however, that any dividends will be paid since they are dependent upon earnings, financial condition and capital requirements of the Company and its subsidiaries as well as policies of the Federal Reserve Board pursuant to the BHCA. See Item 1, “Business, Supervision and Regulation”. As of December 31, 2004, $179.1 million was available for payment of dividends by the Company to its shareholders, under applicable laws and regulations.

      See Note 17 to the consolidated financial statements included in this report for additional information regarding the amount of cash dividends declared and paid on common stock for the three most recent fiscal years.

      As discussed in Note 7 to the consolidated financial statements, in December 1986, the Company declared a dividend distribution of one common share purchase right (the “Right”) for each outstanding share of common stock. The terms of the Rights were most recently amended and restated in 2004. The new amended plan is very similar in purpose and effect to the plan as it existed prior to this amendment, aimed at helping the Board of Directors to maximize shareholder value in the event of a change of control of the Company and otherwise resist actions that the Board considers likely to injure the Company or its shareholders.

Securities Authorized for Issuance Under Equity Compensation Plans

      The following table summarizes the status of the Company’s equity compensation plans as of December 31, 2004 (in thousands, except exercise price):

Issuer Purchases of Equity Securities

      The table below sets forth the information with respect to purchases made by or on behalf of Westamerica Bancorporation or any “affiliated purchaser” (as defined in Rule 10b-18(a)(3) under the Securities Exchange Act of 1934), of common stock during the quarter ended December 31, 2004 (in thousands, except per share data).

      The Company repurchases shares of its common stock in the open market to optimize the Company’s use of equity capital and enhance shareholder value and with the intention of lessening the dilutive impact of issuing new shares to meet stock performance, option plans, and other ongoing requirements.

      Shares were repurchased during the fourth quarter of 2004 pursuant to a program approved by the Board of Directors on August 27, 2004 authorizing the purchase of up to 2 million shares of the Company’s common stock from time to time prior to September 1, 2005. The new 2004 approved amount included 645,429 remaining shares available to be repurchased under the 2003 plan.

      The following financial information for the five years ended December 31, 2004 has been derived from the Company’s Consolidated Financial Statements. This information should be read in conjunction with the Consolidated Financial Statements and related notes thereto included elsewhere herein.

WESTAMERICA BANCORPORATION

FINANCIAL SUMMARY

      The following discussion addresses information pertaining to the financial condition and results of operations of Westamerica Bancorporation and Subsidiaries (the “Company”) that may not be otherwise apparent from a review of the consolidated financial statements and related footnotes.

      It should be read in conjunction with those statements and notes found on pages 42 through 74, as well as with the other information presented throughout the Report.

Critical Accounting Policies

      The Company’s consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States and follow general practices within the banking industry. Application of these principles requires management to make certain estimates, assumptions, and judgments that affect the amounts reported in the financial statements and accompanying notes. These estimates, assumptions, and judgments are based on information available as of the date of the financial statements; accordingly, as this information changes, the financial statements could reflect different estimates, assumptions, and judgments. Certain policies inherently have a greater reliance on the use of estimates, assumptions and judgments and as such have a greater possibility of producing results that could be materially different than originally reported. Estimates, assumptions and judgments are necessary when assets and liabilities are required to be recorded at fair value, when a decline in the value of an asset not carried on the financial statements at fair value warrants an impairment writedown or valuation reserve to be established, or when an asset or liability needs to be recorded contingent upon a future event. Carrying assets and liabilities at fair value inherently results in more financial statement volatility. The fair values and the information used to record valuation adjustments for certain assets and liabilities are based either on quoted market prices or are provided by other third-party sources, when available. When third-party information is not available, valuation adjustments are estimated in good faith by management.

      The most significant accounting policies followed by the Company are presented in Note 1 to the consolidated financial statements. These policies, along with the disclosures presented in the other financial statement notes and in this discussion, provide information on how significant assets and liabilities are valued in the financial statements and how those values are determined. Based on the valuation techniques used and the sensitivity of financial statement amounts to the methods, assumptions, and estimates underlying those amounts, management has identified the Allowance for Loan Losses to be the accounting area that requires the most subjective or complex judgments, and as such could be most subject to revision as new information becomes available.

      The Allowance for Loan Losses represents management’s estimate of the amount of loss in the loan portfolio that can be reasonably estimated as of the balance sheet date. Determining the amount of the Allowance for Loan Losses is considered a critical accounting estimate because it requires significant judgment and the use of estimates related to the amount and timing of expected future cash flows on impaired loans, estimated losses on pools of homogeneous loans based on historical loss experience, and consideration of current economic trends, uncertainties and conditions, all of which may be susceptible to significant change. A discussion of the factors driving changes in the amount of the Allowance for Loan losses is included in the “Credit Quality” discussion below.

OVERVIEW OF FINANCIAL RESULTS

Acquisition

      On August 25, 2004, the Company signed a definitive agreement to acquire Redwood Empire Bancorp, parent company of National Bank of the Redwoods. On January 26, 2005, the Federal Reserve System (“FRB”) approved the Company’s merger application subject to a divestiture of approximately $43 million in

deposits in Lake County. The acquisition was completed on March 1, 2005. After adjusting for the divestiture the transaction was valued at approximately $153 million, including approximately $57 million paid in cash and issuance of the Company’s common stock valued at approximately $85 million, conversion of Redwood Empire stock options into Company stock options with a fair value of about $6 million and certain transaction related costs. During the second half of 2004, the Company reduced the allocation of its operating cash flow toward the repurchase and retirement of its common stock in order to meet the cash payment for the transaction. Further information related to the acquisition, including unaudited pro forma combined financial data, can be found in the Company’s Registration Statement on Form S-4 that was filed with the Securities and Exchange Commission on October 15, 2004.

Net Income

      In the fourth quarter of 2004, the Company recognized a $7.2 million securities impairment writedown to market value of Federal National Mortgage Association (“FNMA”) and Federal Home Loan Mortgage Corporation (“FHLMC”) preferred stock held in the available for sale investment portfolio. The writedown was recorded as a reduction in noninterest income. The after-tax effect was $4.2 million, net of tax benefits of $3.0 million. The decision to record the charge was made because an analysis by management indicated that current market declines in the value of this preferred stock would not recover within a conservative definition of a reasonable period of time. At December 31, 2004, the Company held FNMA and FHLMC preferred stock with an adjusted book value of $63.9 million and a tax-equivalent dividend yield of 7.65%.

      The Company reported net income of $95.2 million in 2004, reflecting a $4.2 million after-tax writedown in the value of FNMA and FHLMC preferred stock, representing a 0.2% increase from the $95.1 million earned in 2003, which was up 9.1% over 2002 earnings of $87.1 million.

      Net income in 2004 was $155 thousand or 0.2% more than in 2003, after including a $4.2 million after-tax government sponsored entity (FNMA and FHLMC) preferred stock impairment charge in 2004. Net interest income (FTE) increased $586 thousand, the net result of higher average earning assets and lower funding costs, partially offset by declining earning asset yields and lower fee income. The loan loss provision declined $600 thousand, year over year, in accordance with Management’s assessment of credit risk for the loan portfolio. Noninterest income fell $4.3 million primarily due to the above impairment charge, partially offset by growth in deposit fee income. Noninterest expense declined $2.9 million because of lower personnel and other operational costs. The lower tax provision (FTE) (down $350 thousand) was due to the $3.0 million tax

benefit of the impairment charge and higher low-income housing investment tax credits, offset in part by increased pretax income.

      Much of the growth in 2003 earnings was attributable to a $6.4 million increase in noninterest income, the result of greater service charge income, and because the 2002 total was reduced by a securities impairment charge of $4.3 million. Net interest income (FTE) increased $1.7 million, the net result of higher average earning assets and lower funding costs, partially offset by declining earning asset yields. The loan loss provision was reduced slightly and noninterest expense declined $1.6 million. The 2002 noninterest expense included $400 thousand in severance costs relating to the acquisition of Kerman State Bank (“KSB”). A $2.0 million increase in the tax provision (FTE) resulted mostly from higher earnings.

      The Company’s return on average total assets was 2.10% in 2004, compared to 2.19% and 2.17% in 2003 and 2002, respectively. Return on average equity in 2004 was 28.83%, compared to 29.38% and 28.70% in 2003 and 2002, respectively.

Net Interest Income

      The Company’s primary source of revenue is net interest income, or the difference between interest income on earning assets and interest expense on interest-bearing liabilities. Net interest income (FTE) in 2004 increased $586 thousand or 0.3% from 2003, to $218.0 million. Comparing 2003 to 2002, net interest income (FTE) increased $1.7 million or 0.8%.

      Interest and fee income (FTE) declined $5.5 million or 2.3% from 2003 to 2004, the net result of declining yields on earning assets and lower loan fee income, partially offset by the effect of higher volume of earning assets. The total yield on earning assets, excluding loan fee income, declined from 5.99% in 2003 to 5.61% in 2004, following the general trend in interest rates within capital markets. The most significant yield declines in the loan portfolio were indirect consumer loans (down 92 basis points (“bp”)), commercial real estate loans (down 37 bp) and residential real estate loans (down 64 bp). Loan fee income, primarily prepayment fees, declined from $3.1 million in 2003 to $1.6 million in 2004, lowering the total earning asset yield an additional 4 bp from 2003. The investment portfolio yield declined 9 bp to 5.07% with declines occurring in U.S. government sponsored entity obligations (down from 3.83% to 3.41%, or 42 bp) and municipal securities (down from 7.14% to 6.80%, or 34 bp). The decline in investment yields was partly mitigated by increases in yields on collateralized mortgage obligations (up 79 bp) and other securities (up 101 bp). The lower yields caused interest income (excluding fees) to decline by $9.2 million, which was offset by the $5.2 million effect of growth in average earning assets (up $202.9 million to $4,236.9 million in 2004). The investment portfolio increased by $298.7 million, primarily the net result of increases in collateralized mortgage obligations (up $247.4 million), municipal securities (up $80.1 million) and U.S. government sponsored entity obligations (up $39.1 million), partially offset by a $60.5 million decline in other securities. The loan portfolio was reduced by $95.8 million with the largest decrease occurring in commercial real estate loans (down $119.5 million).

      Interest expense fell $6.1 million or 22.4% from 2003 to 2004 due to declining rates paid on average interest-bearing liabilities and a change in mix of those liabilities. The average rate paid on interest-bearing liabilities dropped 24 bp to 0.73%. Notable decreases were on money market saving accounts (down 30 bp), CDs over $100 thousand (down 8 bp), retail CDs (down 19 bp) and customer sweep accounts (down 25 bp). Yields on overnight funds purchased increased 26 bp after a series of increases in the target rate for federal funds in the second half of 2004. Interest-bearing liabilities shifted from higher-rate to lower-rate categories. Federal Home Loan Bank (“FHLB”) advances were paid off entirely during 2004, reducing the average balance by $118.1 million. Retail CDs and CDs over $100 thousand fell by $35.8 million and $20.1 million, respectively. Overnight funds purchased and money market accounts rose by $138.5 million and $60.0 million, respectively. A $107.5 million increase in noninterest-bearing balances resulted in the reduction of expense by $1.3 million.

      Interest and fee income (FTE) decreased $10.3 million or 4.0% in 2003 from the previous year, due to the net effect of lower earning asset yields, partially offset by higher average balances of those assets. The total yield on earning assets dropped from 6.81% in 2002 to 6.06% in 2003, reflecting the declining trend in average market rates of interest and a reduction in higher yielding loan totals. The loan portfolio yield declined 65 bp to 6.58%, affected by declines in commercial loan yields (down 39 bp to 6.11%), commercial real estate loan yields (down 34 bp to 7.63%), residential real estate loan yields (down 117 bp to 5.09%), and indirect consumer loan yields (down 110 bp to 6.09%). The investment portfolio yield also fell 72 bp to 5.16%, mainly due to declines in U.S. Treasury securities yields (down 150 bp to 4.13%), U.S. government sponsored entity obligation yields (down 114 bp to 3.83%), mortgage backed securities and collateralized mortgage obligation yields (down 108 bp to 3.33%) and municipal securities yields (down 44 bp to 7.14%).

      Interest expense decreased $12.0 million or 30.6% in 2003 compared to 2002, due to lower interest rates, partly offset by higher average interest-bearing liabilities. The average rate paid on interest-bearing liabilities was 0.97% in 2003, 53 basis points lower than in 2002. Notable declines included money market savings accounts (down 54 bp to 0.75%), Public CDs (down 133 bp to 1.21%), Jumbo CDs (down 69 bp to 1.47%) and short-term borrowings (down 52 bp to 0.89%). Total interest-bearing liabilities grew $190 million or 7.3%, causing a $1.4 million increase in interest expense, mainly due to increases in short-term borrowings (up $129 million or 51.7%) and money market savings accounts (up $101 million or 19.4%). In addition, as a result of continuing marketing efforts to acquire commercial relationships, noninterest-bearing balances increased 9.1%, indirectly causing interest expense to decline an additional $1.0 million.

      The following tables present information regarding the consolidated average assets, liabilities and shareholders’ equity, the amounts of interest income from average earning assets and the resulting yields, and the amount of interest expense paid on interest-bearing liabilities. Average loan balances include nonperforming loans. Interest income includes proceeds from loans on nonaccrual status only to the extent cash payments

have been received and applied as interest income. Yields on securities and certain loans have been adjusted upward to reflect the effect of income exempt from federal income taxation at the current statutory tax rate.

      The following table sets forth a summary of the changes in interest income and interest expense due to changes in average assets and liability balances (volume) and changes in average interest rates for the periods indicated. Changes not solely attributable to volume or rates have been allocated in proportion to the respective volume and rate components.

 Summary of Changes in Interest Income and Expense

Provision for Loan Losses

      The provision for loan losses was $2.7 million for 2004, compared with $3.3 million for 2003 and $3.6 million for 2002. The reductions in the provision reflects Management’s view of credit risk in the loan portfolio and the results of the Company’s continuing efforts to improve loan quality by enforcing strict underwriting and administration procedures and aggressively pursuing collection efforts. For further information regarding net credit losses and the allowance for loan losses, see the “Credit Quality” section of this report.

Investment Portfolio

      The Company maintains a securities portfolio consisting of U.S. Government sponsored entities, state and political subdivisions, asset-backed and other securities. Investment securities are held in safekeeping by an independent custodian.

      The objective of the held to maturity portfolio is to maintain a prudent yield and provide collateral to pledge for federal, state and local government deposits and other borrowing facilities. The held to maturity investment portfolio had a duration of 4.4 years at December 31, 2004 and, on the same date, those investments included $1,118.3 million in fixed-rate and $142.5 million in adjustable-rate securities.

      Investment securities available for sale are generally used to supplement the Company’s liquidity, provide a prudent yield, and provide collateral for public deposits. Unrealized net gains and losses on these securities are recorded as an adjustment to equity, net of taxes, and are not reflected in the current earnings of the Company. If a security is sold, any gain or loss is recorded as a credit or charge to earnings and the equity adjustment is reversed. At December 31, 2004, the Company held $931.7 million in securities classified as investments available for sale with a duration of 3.4 years. At December 31, 2004, an unrealized gain of $9.6 million, net of taxes of $7.0 million, related to these securities, was included in shareholders’ equity.

      The Company had no trading securities at December 31, 2004, 2003 and 2002.

      For more information on investment securities, see Notes 1 and 2 to the consolidated financial statements.

      The following table shows the carrying amount (fair value) of the Company’s investment securities available for sale as of the dates indicated:

      The following table sets forth the relative maturities and yields of the Company’s available for sale securities (stated at amortized cost) at December 31, 2004. Weighted average yields have been computed by dividing annual interest income, adjusted for amortization of premium and accretion of discount, by the

amortized cost value of the related security. Yields on state and political subdivision securities have been calculated on a fully taxable equivalent basis using the current statutory rate.

     Available for Sale Maturity Distribution

      The following table shows the carrying amount (amortized cost) and fair value of the Company’s investment securities held to maturity as of the dates indicated:

     Held to Maturity Portfolio

      The following table sets forth the relative maturities and yields of the Company’s held to maturity securities at December 31, 2004. Weighted average yields have been computed by dividing annual interest income, adjusted for amortization of premium and accretion of discount, by the amortized value of the related security. Yields on state and political subdivision securities have been calculated on a fully taxable equivalent basis using the current statutory rate.

     Held to Maturity Maturity Distribution