FILED BY ORACLE CORPORATION

PURSUANT TO RULE 425 UNDER THE SECURITIES ACT OF 1933

SUBJECT COMPANY: SIEBEL SYSTEMS, INC.

COMMISSION FILE NO. 0-20725

REGISTRATION NO.: 333-129139

[The following was posted to Oracle Corporation’s website]

“Oracle’s recent acquisitions have helped it build a best-of-breed application suite. The proposed Siebel acquisition will extend a proven best of breed CRM solution, which is a market leader. Having worked on multiple global engagements on Oracle, PeopleSoft, Siebel & other applications in the Enterprise space, Infosys is well positioned to help clients chart out a clear map based on their particular situation. Infosys would leverage its partnership with Oracle, its deep domain expertise & its Global Delivery Model to ensure that clients have a more competitive CRM solution with a lower cost of ownership.” —Kakal C—Global Head—Enterprise Solutions.

Important Information

This document may be deemed to be solicitation material in respect of the proposed business combination of Oracle and Siebel Systems. In connection with the proposed transaction, a registration statement on Form S-4 was filed with the SEC on October 19, 2005 (Registration No. 333-129139), containing a proxy statement/prospectus and other documents filed by Oracle and Siebel Systems. STOCKHOLDERS OF SIEBEL SYSTEMS ARE ENCOURAGED TO READ THE REGISTRATION STATEMENT AND ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC, INCLUDING THE PROXY STATEMENT/PROSPECTUS THAT IS PART OF THE REGISTRATION STATEMENT, BECAUSE THEY CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED BUSINESS COMBINATION. The final proxy statement/prospectus will be mailed to stockholders of Siebel Systems. Investors and security holders will be able to obtain the documents free of charge at the SEC’s website, www.sec.gov, from Oracle Corporation, 500 Oracle Parkway, Redwood City, California 94065, Attention: Investor Relations, or from Siebel Systems, Inc., 2207 Bridgepointe Parkway, San Mateo, California 94404, Attention: Investor Relations.

Oracle, Siebel Systems and their respective directors and executive officers and other members of management and employees may be deemed to participate in the solicitation of proxies in respect of the proposed transactions. Information regarding Oracle’s directors and executive officers is available in Oracle’s proxy statement for its 2005 annual meeting of stockholders, which was filed with the SEC on August 30, 2005, and information regarding Siebel Systems’ directors and executive officers is available in Siebel Systems’ proxy statement for its 2005 annual meeting of stockholders, which was filed with the SEC on April 29, 2005. Additional information regarding the interests of such potential participants will be included in the proxy statement/prospectus and the other relevant documents filed with the SEC when they become available.

Cautionary Statement Regarding Forward-Looking Statements

This document contains certain forward-looking statements about Oracle and Siebel Systems. When used in this document, the words “anticipates”, “may”, “can”, “believes”, “expects”, “projects”, “intends”, “likely”, similar expressions and any other statements that are not historical facts, in each case as they relate to Oracle and Siebel Systems, the management of either such company or the transaction are intended to identify those assertions as forward-looking statements. In making any such statements, the person making them believes that its expectations are based on reasonable assumptions. However, any such statement may be influenced by factors that could cause actual outcomes and results to be materially different from those projected or anticipated. These forward-looking statements are subject to numerous risks and uncertainties. There are various important factors that could cause actual results to differ materially from those in any such forward-looking statements, many of which are beyond the control of Oracle and Siebel Systems, including: the impact of general economic conditions in regions in which either such company currently does business, industry conditions, including competition, fluctuations in exchange rates and currency values, capital expenditure requirements, legislative or regulatory requirements, changes in the tax laws, interest rates and access to capital markets. The actual results or performance by Oracle or Siebel Systems could differ materially from those expressed in, or implied by, these forward-looking statements. Accordingly, no assurances can be given that any of the events anticipated by the forward-looking statements will transpire or occur, or if any of them do so, what impact they will have on the results of operations or financial condition of Oracle or Siebel Systems.