Filed by Chevron Corporation
pursuant to Rule 425 under the Securities Act of 1933
and deemed filed pursuant to Rule 14a-12
under the Securities and Exchange Act of 1934, as amended

Subject Company: Unocal Corporation
Commission File No.: 1-8483

July 19, 2005 Chevron and Unocal New Terms

Cautionary Statement CAUTIONARY STATEMENTS RELEVANT TO FORWARD-LOOKING INFORMATION FOR THE PURPOSE OF "SAFE HARBOR" PROVISIONS OF THE PRIVATE SECURITIES LITIGATION REFORM ACT OF 1995 Except for the historical and factual information contained herein, the matters set forth in this presentation, including statements as to the expected benefits of the acquisition such as efficiencies, cost savings, market profile and financial strength, and the competitive ability and position of the combined company, and other statements identified by words such as "expects," "projects," "plans," and similar expressions are forward-looking statements within the meaning of the "safe harbor" provisions of the Private Securities Litigation Reform Act of 1995. These forward-looking statements are subject to risks and uncertainties that may cause actual results to differ materially, including required approvals by Unocal shareholders and regulatory agencies, the possibility that the anticipated benefits from the acquisition cannot be fully realized, the possibility that costs or difficulties related to the integration of our businesses will be greater than expected, the impact of competition and other risk factors relating to our industry as detailed from time to time in each of Chevron's and Unocal's reports filed with the SEC. You should not place undue reliance on these forward-looking statements, which speak only as of the date of this presentation. Unless legally required, Chevron and Unocal undertake no obligation to update publicly any forward-looking statements, whether as a result of new information, future events or otherwise.

New Terms of Transaction 60% Tax-free exchange of stock at ratio: 1.03 Chevron: 1 Unocal 40% Cash at $69 for each Unocal share Value of transaction $17.1 billion in cash and stock ($17.9 billion including estimated Unocal net debt) At the July 19 CVX closing price, the 60/40 blended value is $63.01 per Unocal share Principal condition to close is Unocal shareholders' approval

New Financial Impact Cashflow per share accretion: 6-7% EPS accretion: ~2% ROCE dilution: 1-2% Intend to remain top tier on ROCE Adds value on an economic return basis

Additional Information and Where to Find It Chevron has filed a Form S-4, Unocal has filed a proxy statement and both companies will file other relevant documents concerning the proposed merger transaction with the Securities and Exchange Commission (SEC). INVESTORS ARE URGED TO READ THE FORM S-4, PROXY STATEMENT AND ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC BECAUSE THEY CONTAIN IMPORTANT INFORMATION. You may obtain the documents free of charge at the website maintained by the SEC at www.sec.gov. In addition, you may obtain documents filed with the SEC by Chevron free of charge by contacting Chevron Comptroller's Department, 6001 Bollinger Canyon Road - A3201, San Ramon, CA 94583-2324. You may obtain documents filed with the SEC by Unocal free of charge by contacting Unocal Stockholder Services at (800) 252-2233, 2141 Rosecrans Avenue, Suite 4000, El Segundo, CA 90245, e-mail: stockholder_services@unocal.com. Interest of Certain Persons in the Merger Chevron, Unocal, and their respective directors and executive officers, may be deemed to be participants in the solicitation of proxies from Unocal's stockholders in connection with the merger. Information about the directors and executive officers of Chevron and their ownership of Chevron stock is set forth in the proxy statement for Chevron's 2005 Annual Meeting of Stockholders. Information about the directors and executive officers of Unocal and their ownership of Unocal stock is set forth in the proxy statement for Unocal's 2005 Annual Meeting of Stockholders. Investors may obtain additional information regarding the interests of such participants by reading the Form S-4 and proxy statement for the merger. Investors should read the Form S-4 and proxy statement carefully before making any voting or investment decisions.