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QUESTIONS AND ANSWERS ABOUT THE MERGER

Q:	What will happen to Redwood Empire Bancorp and National Bank of the Redwoods in this merger?
A:	Redwood Empire Bancorp will merge with Westamerica Bancorporation, with Westamerica Bancorporation as the surviving corporation. Promptly after that National Bank of the Redwoods will merge with Westamerica Bank. The resulting bank will continue under the name “Westamerica Bank” as a wholly owned subsidiary of Westamerica Bancorporation. The existing branches of National Bank of the Redwoods willeitherbecome or be consolidated with branches of Westamerica Bank.
Q:	How do I vote?
A:	Simply indicate on your proxy card how you want to vote and then sign and mail your proxy card in the enclosed return envelope as soon as possible so that your shares may be represented at the Redwood Empire Bancorp special meeting.
Q:	If my shares are held in “street name” by my broker, will my broker vote my shares for me?
A:	Your broker will not vote your shares for you unless you provide instructions to your broker on how to vote. It is important therefore that you follow the directions provided by your broker regarding how to instruct your broker to vote your shares. If you fail to instruct your broker how to vote your shares, the effect will be the same as a vote against the merger agreement.
Q:	Can I change my vote after I have mailed my signed proxy card?
A:	Yes. You may change your vote at any time before your proxy is voted at the special meeting. If your shares are held in your name you may do this in one of three ways. First, you may send a written notice stating that you would like to revoke your proxy. Second, you may complete and submit a new proxy card. If you choose either of these two methods, Redwood Empire Bancorp must receive your notice of revocation or your new proxy card to Redwood Empire Bancorp at the address at the top of the Notice of Special Meeting prior to the vote at the special meeting. Third, you may revoke your proxy before it is exercised by attending the special meeting and electing to vote in person. If you have instructed a broker to vote your shares, you must follow directions received from your broker to change your vote or to vote at the Redwood Empire Bancorp special meeting.
Q:	Should I send in my certificates now?
A:	No. After the merger is completed, we will send you written instructions for exchanging your stock certificates.
Q:	When do you expect this merger to be completed?
A:	We are working toward completing this merger as quickly as possible. We currently expect, subject to receiving required regulatory approvals, to complete this merger in the fourth quarter of 2004 or the first quarter of 2005.

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SUMMARY

This summary, together with the “Questions and Answers” on the preceding pages, highlights important selected information from this proxy statement/prospectus. To understand the merger fully and for a more complete description of the legal terms of the merger, you should read carefully this entire document and the other information available to you. We have included page references in parentheses to direct you to a more complete description of the topics presented in this summary.

Redwood Empire Bancorp shareholders will receive $28.74, consisting of $11.49 in cash and $17.25 in shares of Westamerica Bancorporation common stock in the merger, but this amount is subject to possible adjustment (page 44)

     If the merger is completed, each share of Redwood Empire Bancorp common stock will be converted into the right to receive merger consideration of $28.74, consisting of $11.49 in cash and $17.25 in shares of Westamerica Bancorporation common stock, valued at its average closing price for the 20 trading days ending three business days before the effective date of the merger. The merger consideration may be reduced by up to $0.30 per share (allocated proportionately between cash and stock) if bank regulators require Westamerica Bancorporation or Redwood Empire Bancorp to divest deposits in Lake County as a condition of approving the merger. For example, based on an assumed Westamerica average closing price of $55.25 (the average closing price for the 20 trading days ended October 11, 2004) and a resulting exchange ratio of 0.3122, if you held 100 shares of Redwood Empire Bancorp common stock, you would have the right to receive $1,149 in cash and 31.22 shares of Westamerica Bancorporation common stock in the merger (assuming no adjustments). You will receive cash instead of fractional shares. Therefore, you would only receive 31 shares of Westamerica Bancorporation common stock. You would also receive a check in an amount equal to 0.22 of a share multiplied by an average closing price of the Westamerica Bancorporation common stock on account of your fractional share, or $12.16 based on an average closing price of $55.25.

The following table shows the effect on the exchange ratio and the value of the merger consideration of changes in the average closing price of Westamerica Bancorporation common stock (rounded to the nearest cent):

     The merger agreement may be terminated by the board of directors of Redwood Empire Bancorp if Westamerica’s average closing price is less than $40.44. The merger agreement may be terminated by the board of directors of Westamerica Bancorporation if Westamerica Bancorporation’s average closing price is greater than $60.66.

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The merger consideration will be reduced if Westamerica Bancorporation is required to divest deposits in Lake County as a condition of any governmental approval of the merger. Any reduction will be allocated proportionately between the stock portion and the cash portion. The following table shows the effect of deposit divestitures on the value of the merger consideration (assuming no adjustment on account of a change in Westamerica’s average closing price).

The following table shows the effect on the exchange ratio and the value of the merger consideration of changes in the average closing price of Westamerica Bancorporation common stock, assuming a required divestiture of more than $30 million in deposits in Lake County:

If Westamerica Bancorporation is required to divest at least $10 million but not more than $30 million in deposits, the reductions in the exchange ratio, value of the stock portion and the total merger consideration would be proportionately less. For additional detail on the effect of these possible adjustments, see “The merger agreement — Conversion of Redwood Empire Bancorp common stock” on page 44.

Comparative Market Price Data

     Westamerica Bancorporation’s common stock is traded on the Nasdaq National Market under the symbol “WABC.” Redwood Empire Bancorp common stock is traded on the Nasdaq National Market under the symbol “REBC.”

     The following table presents historical per share market values for Westamerica Bancorporation common stock and Redwood Empire Bancorp common stock and the equivalent pro forma market values (i) on August 25, 2004, the last trading day prior to public announcement of the merger and (ii) on [                    , 2004]. The historical values represent the last sale prices on or before the dates indicated. The equivalent pro forma market value of Redwood Empire Bancorp common stock is obtained by multiplying the historical market price of Westamerica Bancorporation common stock by the applicable exchange ratio. The equivalent pro forma market value per share of Redwood Empire Bancorp common stock assumes an average closing price equivalent to the market price for Westamerica Bancorporation common stock shown in the table and an assumed exchange ratio of 0.3122 (the actual exchange ratio will vary) and no adjustments on account of a possible divestiture of deposits.

     The values shown for Westamerica Bancorporation common stock may be higher or lower than the average closing price of Westamerica Bancorporation common stock as that term is defined in the merger agreement for purposes of determining the exchange ratio and the actual market value of Westamerica Bancorporation common stock at the time of completion of the merger, so the market value of Westamerica

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Once Redwood Empire Bancorp is acquired by Westamerica Bancorporation, there will be no further public market for Redwood Empire Bancorp’s common stock. Westamerica Bancorporation common stock will continue to be traded on the Nasdaq National Market.

The merger is intended to be a tax-free transaction in which Redwood Empire Bancorp shareholders will not recognize gain or loss on the stock portion of the merger consideration (page 38)

The merger is intended to be a tax-free reorganization so that no gain or loss will be recognized by either Westamerica Bancorporation or Redwood Empire Bancorp or their respective shareholders for federal income tax purposes on the stock portion of the merger consideration. Redwood Empire Bancorp shareholders may recognize gain but not loss on the receipt of the cash portion of the merger consideration.

Redwood Empire Bancorp’s board recommends shareholder approval (pages 18, 22)

Redwood Empire Bancorp’s board of directors believes that the merger is in the best interests of Redwood Empire and its shareholders and has unanimously approved the merger agreement. Redwood Empire Bancorp’s board unanimously recommends that you vote “FOR” approval of the merger agreement.

Vote Required (page 19)

     Approval of the merger by Redwood Empire Bancorp shareholders requires the affirmative vote of the holders of a majority of the outstanding shares. The directors and executive officers of Redwood Empire Bancorp and their affiliates together held approximately 1.0% of Redwood Empire’s outstanding common stock as of the record date. You should be aware that Redwood Empire Bancorp shareholders holding approximately 49.6% of the outstanding shares have agreed to vote in favor of the merger and have given Westamerica Bancorporation irrevocable proxies to vote their shares in favor of the merger and that directors of Redwood Empire, who in the aggregate own approximately 1.0% of the outstanding shares, have also agreed to vote their shares in favor of the merger. Therefore shareholder approval of the merger is effectively assured.

The merger does not require the approval of the shareholders of Westamerica Bancorporation.

Financial advisor has given an opinion that consideration is fair to Redwood Empire Bancorp shareholders (page 25)

In deciding to approve the merger, the Redwood Empire Bancorp board of directors considered the opinion of its financial advisor, Hovde Financial LLC, dated as of August 13, 2004, about the fairness of the merger to Redwood Empire Bancorp shareholders from a financial point of view. This opinion is attached as Annex B to this proxy statement/ prospectus. We encourage you to read it carefully. Under an agreement with Redwood Empire Bancorp, Hovde Financial LLC will receive a fee of approximately $1,530,000, subject to adjustment depending on the actual value of the merger consideration as of closing, when the merger closes.

Dissenters’ rights of appraisal (page 40 and Annex C)

     You will be given the opportunity to exercise dissenters’ rights in accordance with certain procedures specified under California law, provided that demands are made for payment with respect to 5% or more of the outstanding shares of Redwood Empire Bancorp common stock. This means that shareholders who vote against the merger may make a written demand to Redwood Empire Bancorp for payment in cash of the “fair market value” of their shares. Redwood Empire Bancorp must receive the demand no later than the date of the special meeting. To exercise dissenters’ rights, you must vote shares against the merger; it is not sufficient

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Benefits to certain officers and directors in the merger (page 35)

     In considering the recommendation of the board of directors of Redwood Empire Bancorp to approve the merger agreement, you should be aware that certain executive officers and directors of Redwood Empire Bancorp have certain interests in, and will receive benefits as a consequence of, the merger that are different from the benefits to Redwood Empire Bancorp shareholders generally. These interests include:

	•	vesting of all outstanding stock options, which, based on anticipated holdings as of December 1, 2004 and merger consideration of $28.74, would result in an estimated aggregate benefit to executive officers and directors of approximately $508,150; and
	•	potential severance benefits available to executive officers and directors under various severance policies, change in control agreements and salary continuation agreements, which could result in cash severance payments to executive officers and directors, assuming all were terminated immediately following the merger, of approximately $1,670,055 in the aggregate.

Shareholders of Westamerica Bancorporation and Redwood Empire Bancorp have different rights (page 69)

The rights of holders of Westamerica Bancorporation common stock are different in some respects from the rights of holders of Redwood Empire Bancorp common stock. You should consider these differences when voting on the merger.

Information regarding Westamerica Bancorporation and Redwood Empire Bancorp (pages 21, 54 and 64)

	Westamerica Bancorporation 4550 Mangels Boulevard Fairfield, CA 94585-1200 [(415) 257-8000] www.westamerica.com

     Westamerica Bancorporation is a bank holding company registered under the Bank Holding Company Act of 1956. Westamerica Bancorporation was incorporated under the laws of the State of California as “Independent Bankshares Corporation” on February 11, 1972. It is the parent of Westamerica Bank and Community Banker Services Corporation. Westamerica Bancorporation has 88 branches throughout northern and central California. Westamerica Bancorporation as of June 30, 2003, was the 14th largest bank and 18th largest depository institution, measured by deposits, in California. At June 30, 2004 it had total assets of $4.6 billion, deposits of approximately $3.5 billion and shareholders’ equity of $329.8 million.

	Redwood Empire Bancorp 111 Santa Rosa Avenue Santa Rosa, CA 95404 (707) 573-4800

     Redwood Empire Bancorp is a bank holding company registered under the Bank Holding Company Act of 1956. It was originally incorporated in 1988 for the purpose of becoming the holding company of National Bank of the Redwoods, a national banking association founded in 1985. Redwood Empire Bancorp conducts a general commercial banking business through its main office in Santa Rosa, California, five retail branches located in Sonoma County, California, one retail branch located in Mendocino County, California, and one retail branch located in Lake County, California. At June 30, 2004, Redwood Empire Bancorp had assets of

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Special shareholders meeting to be held on [meeting date], 2004 (page 18)

We will hold the special meeting of shareholders of Redwood Empire Bancorp at [meeting time] on Thursday, [meeting date], 2004, at Redwood Empire Bancorp, 111 Santa Rosa Avenue, Santa Rosa, California 95404. At the special meeting, you will be asked (1) to approve the merger agreement and (2) to consider such other business as may properly come before the meeting.

Record date set at [record date], 2004; vote required for approval of merger (page 19)

You can vote at the special meeting if you owned Redwood Empire Bancorp common stock at the close of business on [record date], 2004. Holders of a majority of the outstanding shares of Redwood Empire Bancorp common stock must vote to approve the merger agreement in order for the merger to occur.

Conditions that must be satisfied for the merger to occur (page 51)

     We will not complete the merger unless a number of conditions are met. These include:

	•	approval of the merger agreement by Redwood Empire Bancorp shareholders,
	•	receipt of all required regulatory approvals;
	•	absence of material adverse changes in the parties, unless waived; and
	•	satisfaction by Redwood Empire Bancorp of certain financial conditions relating to its levels of performing loans, noninterest-bearing deposits and shareholders’ equity, unless waived by Westamerica Bancorporation.

Regulatory approvals we must obtain for the merger to occur (page 34)

The merger requires the prior approval of the Board of Governors of the Federal Reserve System (the “FRB”) under the Bank Merger Act and of the California Department of Financial Institutions under the California Financial Code. The FRB may require Westamerica Bancorporation or Redwood Empire Bancorp to divest deposits in Lake County as a condition to its approval. If such divestiture is required, the merger consideration could be reduced by up to $0.30 per share.

Westamerica Bancorporation to use purchase accounting treatment (page 38)

Westamerica Bancorporation will account for the merger as a purchase. Under the purchase accounting method, Westamerica Bancorporation will revalue on its books the assets and liabilities of Redwood Empire Bancorp at their fair market values, and the amount by which the aggregate merger consideration exceeds the net fair values of the assets of Redwood Empire Bancorp will be recorded as intangibles such as goodwill or core deposit intangible.

Termination of the merger agreement (page 52)

     The merger agreement may be terminated before completion as follows:

	•	by the mutual consent of Redwood Empire Bancorp and Westamerica Bancorporation;
	•	by either party if the conditions to its obligations have not been met by May 25, 2005;
	•	by either party if the shareholders of Redwood Empire Bancorp fail to approve the merger agreement at the Special Meeting;
	•	by either party if the other fails to comply materially with its obligations under the merger agreement and fails to cure within 60 days;
	•	by either party if any necessary governmental approval has been denied;
	•	by Westamerica Bancorporation if Redwood Empire Bancorp materially breaches its obligation not to solicit or encourage a different transaction for the acquisition of Redwood Empire Bancorp, and, in the

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		event of such termination, Redwood Empire Bancorp will be liable to Westamerica Bancorporation for a break-up fee of $4,500,000;
	•	by Westamerica Bancorporation if the board of directors of Redwood Empire Bancorp fails to recommend adoption of the merger agreement at the special meeting, and, in the event of such termination, Redwood Empire Bancorp will be liable to Westamerica Bancorporation for a break-up fee of $4,500,000;
	•	by Redwood Empire Bancorp if its board of directors authorizes it to enter into a superior transaction for the acquisition of Redwood Empire Bancorp, and, in the event of such termination, Redwood Empire Bancorp will be liable to Westamerica Bancorporation for a break-up fee of $4,500,000;
	•	by either party if Westamerica Bancorporation solicits or encourages an acquisition of Westamerica Bancorporation that would materially interfere with its obligations under the merger agreement, and, in the event of such termination, Westamerica Bancorporation will be liable to Redwood Empire Bancorp for a break-up fee of $4,500,000;
	•	by Westamerica Bancorporation if the Westamerica average closing price is greater than $60.66; and
	•	by Redwood Empire Bancorp if the Westamerica average closing price is less than $40.44.

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Selected Financial Information About Westamerica Bancorporation

The following table presents selected supplemental historical financial information for Westamerica Bancorporation for each of the five years in the period ended December 31, 2003, and the six-month periods ended June 30, 2004 and 2003. This information has been derived from and should be read in conjunction with the supplemental consolidated financial statements of Westamerica Bancorporation, including the notes to such financial statements, which are incorporated by reference elsewhere in this document.

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*	Fully taxable equivalent

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Selected Financial Information About Redwood Empire Bancorp

The following table presents selected supplemental historical financial information for Redwood Empire Bancorp for each of the five years in the period ended December 31, 2003, and the six-month periods ended June 30, 2004 and 2003. This information has been derived from and should be read in conjunction with the supplemental consolidated financial statements of Redwood Empire Bancorp including the notes to such financial statements, which are incorporated by reference elsewhere in this document.

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(1)	Restated for 2001 and 2003 3 for 2 stock splits.
(2)	Amounts previously reported as an extraordinary loss for the year ended December 31, 1999 have been reclassified to other expense in order to comply with FASB Statement No. 145. The related ratios and per share data have been restated to give effect to this reclassification.
(3)	Ratios for the six months ended June 30, 2004 and 2003 are annualized.

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Selected Consolidated Unaudited Pro Forma Financial Information

     The following table shows information about our financial condition and results of operations, including per share data and financial ratios, after giving effect to the merger. This information is called pro forma financial information in this document. The table sets forth the information as if the merger had become effective on June 30, 2004, with respect to financial condition data, and on January 1, 2003, with respect to results of operations data. This pro forma financial information assumes that the merger is accounted for using the purchase method of accounting and represents a current estimate based on available information of the combined company’s results of operations. See “Accounting Treatment” on page 38. The pro forma information is based on an assumed Westamerica average closing price of $55.25 (the average closing price for the 20 trading days ended October 11, 2004) and a corresponding exchange ratio of 0.3122. The pro forma financial information includes adjustments to record the assets and liabilities of Redwood Empire Bancorp at their estimated fair values and is subject to further adjustment as additional information becomes available and as additional analyses are performed. The pro forma financial statements do not currently include costs that will be incurred by Westamerica Bancorporation after completion of the merger to combine the operations of Westamerica Bancorporation and Redwood Empire Bancorp. This table should be read in conjunction with, and is qualified in its entirety by, the historical financial statements, including the notes thereto, of Westamerica Bancorporation and Redwood Empire Bancorp incorporated by reference in this document and the more detailed pro forma financial information, including the notes thereto, appearing elsewhere in this document. See “Where You Can Find Additional Information” on page 78 and “Unaudited Pro Forma Condensed Combined Financial Information” on page 71.

     The pro forma financial information, while helpful in illustrating the financial characteristics of the combined company under one set of assumptions, does not reflect the impact of possible revenue enhancements, expense efficiencies, asset dispositions and share repurchases, among other factors, that may result as a consequence of the merger and, accordingly, does not attempt to predict or suggest future results. It also does not necessarily reflect what the historical results of the combined company would have been had our companies been combined during these periods.

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Selected Consolidated Unaudited Pro Forma Financial Information

* Fully taxable equivalent

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Selected Consolidated Unaudited Pro Forma Financial Information