press release

Unocal announces successful Champlain deepwater appraisal well in Gulf of Mexico

Sugar Land, Texas, July 21, 2003 -- Unocal Corporation (NYSE: UCL) today announced the successful completion of drilling operations at the No. 4 well on the Champlain discovery.

The well, located in Atwater Valley 63, was drilled to a total vertical subsea depth of 27,869 feet.

The well was drilled in 4,418 feet of water using the Discoverer Spirit drillship. Operations were completed in 78 days at a gross cost of $41.8 million.

The well encountered more than 200 net feet of hydrocarbon pay. Extensive pressure and fluid sampling was conducted successfully. The current focus is on potential development concepts, and Unocal and its co-venturers are now working on a forward plan for the project.

"The positive appraisal of the Champlain discovery, together with first production from Mad Dog and K2 targeted for early 2005, and advancement of development planning at Trident, provides us with a growing backlog of development projects in the deepwater Gulf of Mexico," said Mike Bell, vice president of Unocal Deepwater USA.

Unocal has a 30 percent working interest in the Champlain discovery. Its co-venturers are ChevronTexaco (NYSE CVX), the operator (20%); Eni Petroleum (NYSE: E) (37.5%); and BHP Billiton Petroleum (Deepwater) Inc.(NYSE: BHP) (12.5%).

Bell said the company's backlog of projects would positively impact near-to-medium term production and reserves.

Deepwater GOM drilling program

Unocal also said that its drilling schedule in the deepwater Gulf of Mexico for the remainder of the year would be focused on prospects adjacent to recent industry successes.

"Our drill schedule for the remainder of the year includes three high-potential wildcats, all following up on industry successes," Bell said.

Drilling operations have begun on the company's St. Malo prospect in Walker Ridge, using the Discoverer Spirit drillship.

The well, Walker Ridge 678 #2, will test the deeper Eocene and Paleocene sections, where hydrocarbons have been found at the neighboring Cascade and Chinook prospects.

Unocal is operator and holds a 33.75-percent working interest in the St. Malo prospect. Co-venturers include Petrobras (PBR.N) (PETR4.SA), 25-percent interest; ChevronTexaco Corporation (NYSE: CVX), 12.5 percent interest; Devon Energy Corporation (AMEX: DVN), 12.5-percent interest; Ocean Energy (a unit of Devon), 10-percent interest; and EnCana Corporation (NYSE: ECA), 6.25-percent interest.

Upon completion of the St. Malo well, the drillship is scheduled to move on to the North Brontosaurus prospect in Alaminos Canyon block 731, a structure adjacent to and saddle-separated from the company's Trident discovery in Alaminos Canyon block 903. Development scenarios at Trident will be influenced by drilling results in the area, the company said.

Following this, drilling will begin at Myrtle Beach in Green Canyon block 943, a prospect located 6 blocks southwest of ChevronTexaco's Tahiti discovery.

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 Unocal's future exploration 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 factors discussed in Unocal's 2002 Annual Report on Form 10-K and subsequent reports filed with the Securities and Exchange Commission.

U.S. investors are urged to consider closely the disclosure in Unocal's 2002 Annual Report on Form 10-K (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: July 2003