press release

Unocal makes major deepwater discovery on St. Malo prospect in Gulf of Mexico

Sugar Land, Texas, Oct. 29, 2003 - Unocal Corporation (NYSE: UCL) today said it has made a major hydrocarbon discovery on the deepwater St. Malo prospect in Walker Ridge block 678 in the Gulf of Mexico.

The discovery well encountered more than 450 net feet of oil pay over a gross hydrocarbon column of 1,400 feet, indicating that St. Malo is a major hydrocarbon accumulation.

The company said that it expects to begin an appraisal program in early 2004, based on the current evaluation of resource potential. "The potential volumes at St. Malo give us the confidence to call this discovery a significant milestone in our Gulf of Mexico deepwater program," said Mike Bell, Unocal's vice president for the Deepwater USA unit. "St. Malo represents a valuable addition to our portfolio of discoveries, and we have excellent leverage in this emerging play with a robust portfolio of projects and leads in the Keathley Canyon, Green Canyon and Walker Ridge areas."

The St. Malo well spud on July 6 and was drilled to a depth of 29,066 feet in 100 days at an estimated gross cost of $62 million. The well is located in 6,900 feet of water about 250 miles south-southwest of New Orleans. The well was drilled from the Discoverer Spirit drillship.

Unocal is the operator and holds a 28.75-percent working interest in the prospect. Unocal's co-venturers in the St. Malo prospect are Petrobras (NYSE: PBR), 25 percent; Devon Energy Corporation (AMEX: DVN), 22.5 percent; ChevronTexaco Corporation (NYSE: CVX), 12.5 percent; EnCana Gulf of Mexico LLC (NYSE: ECA), 6.25 percent; ExxonMobil (NYSE: XOM), 3.75 percent; and Eni Petroleum, 1.25 percent.

Upon completion of the St. Malo well, the Discoverer Spirit will be released to move on to the ExxonMobil Hawkes appraisal well in Mississippi Canyon 508.

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 certain forward-looking statements about future drilling plans. These statements are not guarantees of future performance. The statements are based upon Unocal's current expectations and beliefs and are subject to a number of known and unknown risks and uncertainties that could cause actual results to differ materially from those described in the forward-looking statements. Actual results could differ materially as a result of changes in commodity prices; the levels of the company's oil and gas production; the extent of the company's operating cash flow and other capital resources available to fund its capital expenditures; regulatory, geological, operating and economic considerations; and other factors discussed in Unocal's 2002 Annual Report on Form 10-K and subsequent reports filed with the U.S. Securities and Exchange Commission. Unocal undertakes no obligation to update the information in this news release.

Investors are urged to consider closely the disclosure in Unocal's 2002 Annual Report on Form 10-K and other reports filed with the SEC (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,

Updated: October 2003