press release

Unocal begins common stock repurchase program

El Segundo, Calif., Aug. 4, 2004 - Unocal Corporation (NYSE: UCL) said today that it has commenced repurchases of its shares of common stock pursuant to its previously announced repurchase program. Unocal also announced that it has made the $100 million voluntary contribution to its U.S. pension plan included as part of the previously announced cash expenditures program.

About Unocal Corporation

Unocal is one of the world's leading independent natural gas and crude oil exploration and production companies. The company's principal oil and gas activities are in North America and Asia.

This news release contains forward-looking statements about Unocal's common stock repurchase program. Although these statements are based upon Unocal's current expectations and beliefs, they are subject to known and unknown risks and uncertainties that could cause actual results and outcomes to differ materially from those described in, or implied by, the forward-looking statements, including market conditions for the company's common stock; changes in commodity prices and the effectiveness of the company's hedging activities to manage that volatility; the company's ability to find or acquire additional oil and gas reserves and to develop deepwater fields and other large projects in a timely and cost-effective manner; the accuracy of the company's estimates and judgments regarding hydrocarbon resources and formations; decline rates of producing properties in which the company has an interest; adverse geological and other operational factors; the extent of the company's operating cash flow and other capital resources available to fund its capital expenditures; international and domestic regulatory, political, and economic considerations, including regulations that may affect the repurchases of the company's securities; performance by third parties, including foreign government entities, joint venture partners, independent contractors and operators of properties in which the company has an interest; and other factors discussed in Unocal's 2003 Annual Report on Form 10-K, as amended, and subsequent reports filed by Unocal with the Securities and Exchange Commission (SEC File No. 1-8483). Copies of the company's SEC filings are available from the company by calling 800-252-2233 or from the SEC by calling 800-SEC-0330. The reports are also available on the Unocal web site. Unocal undertakes no obligation to update the forward-looking statements in this news release to reflect future events or circumstances. All such statements are expressly qualified in their entirety by this cautionary statement.

Updated: August 2004