press release

Unocal's Vietnam units file declaration of commercial discovery for offshore natural gas fields; anticipate development

El Segundo, Calif., May 15, 2002 - Unocal Corporation (NYSE: UCL) today said that its Vietnam subsidiaries have filed a declaration of commercial discovery with PetroVietnam, the state oil company, for three natural gas fields offshore southwest Vietnam.

The declaration comes after a string of 10 successful exploration wells drilled on blocks B and 52/97, including four wells drilled last year.

"Our drilling results show that there are sufficient resources on the blocks to support major new power development projects in Vietnam with clean-burning natural gas," said Randy L. Howard, Unocal vice president for International Energy Operations. "This declaration is the first step toward signing a long-term gas sales agreement, which is required before any field development can begin."

The declaration covers resources that have been discovered in the Kim Long, Ac Quy and Ca Voi natural gas fields. Based on the drilling to date, Unocal believes the fields have a combined gross discovery volume of 2.5 trillion cubic feet (tcf) of gas. This resource volume is in a core area that would allow the three fields to be developed in a single program using shared offshore facilities.

Unocal estimates the gross unrisked resource potential, including predicted field extensions and yet undrilled prospective trends, for the combined contract areas (Blocks B, 52/97 and 48/95) at 5 to 8 tcf. More drilling is planned.

"We will now look to a certification of the gas reserves by the government of Vietnam later this year," said John M. Parmigiano, president of Unocal Vietnam, Ltd.

Parmigiano added that EVN (Vietnam's state electricity company) and Unocal will soon begin a pre-feasibility study for an electricity generating plant that would be built at O Mon in the central Mekong Delta. PetroVietnam and Unocal are also completing an initial study on a 236-mile-long (380-kilometer) pipeline from the offshore gas fields to O Mon.

Exploration drilling results

Unocal drilled four wells on the offshore prospects in latest exploration program.

The B-KL-4X well on the Kim Long field encountered 300 feet (92m) of net gas pay, the highest among the four wells drilled on the field so far.

The 52/97-CV-3X well extended the Ca Voi field. The well encountered 151 feet (46m) of net gas pay and was flow tested at 37 million cubic feet (mmcf) per day from four zones.

Two discovery wells extended the Ac Quy field. The 52/97-AQ-4X well encountered 117 feet (35m) of net gas pay and flowed at 48 mmcf per day from four zones. The 52/97-AQ-5X well encountered 301 feet (92m) of gas pay.

Unocal and its co-venturers

Unocal and its co-venturers have signed two production-sharing contracts (PSCs) with PetroVietnam covering Blocks B, 48/95 and 52/97 offshore southwestern Vietnam. Unocal subsidiaries serve as operator for all three PSC areas. Other co-venturers include subsidiaries of Mitsui Oil Exploration Company (MOECO) of Japan and PTT Exploration and Production Public Company Limited (PTTEP) of Thailand. PetroVietnam, through its subsidiary PetroVietnam Exploration and Production Company (PVEP), holds working interests in Blocks B and 48/95 and the rights to acquire additional interest in both PSCs.

As a result of the declaration of commercial discovery, PetroVietnam may exercise its option to convert its carried participating interests into paying working interests. Should PetroVietnam opt to convert to normal working interests, Unocal Vietnam Exploration, Ltd., would hold a 42.38-percent working interest in Blocks B & 48/95 and Unocal's Southwest Vietnam Exploration & Production, Ltd., subsidiary would have a 43.4-percent working interest in Block 52/97. MOECO would hold 25.62 percent in Blocks B and 48/95 and 19.6 percent in Block 52/97. PTTEP would hold 8.5 percent in Blocks B and 48/95 and 7.0 percent in Block 52/97. PetroVietnam through its PVEP subsidiary would hold 23.5 percent in Blocks B and 48/95 and 30 percent in Block 52/97.

About Unocal Corporation

Unocal is one of the world's leading independent natural gas and crude oil exploration and production companies. The company's oil and gas activities are in North America, Asia, Latin America, the North Sea, and West Africa. Unocal is one of the world's largest producers of geothermal energy with operations in the Philippines and Indonesia.

This news release contains certain forward-looking statements about Unocal's possible development activities, business agreements, discovery volume and resource potential. Discovery volume and resource potential are speculative estimates of ultimate recovery (including non-proved resource) based on engineering, geophysical, and geological studies and may include market risk. 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 2001 Annual Report on Form 10-K and subsequent reports filed with the Securities and Exchange Commission.

Cautionary Note to U.S. Investors: The U.S. Securities and Exchange Commission permits oil and gas companies, in their filings with the SEC, to disclose only proved reserves that a company has demonstrated by actual production or conclusive formation tests to be economically and legally producible under existing economic and operating conditions. Unocal uses certain terms in this news release, such as "discovery volume" and "resource potential," that the SEC's guidelines strictly prohibit Unocal from including its filings with the SEC. U.S. investors are urged to consider closely the disclosure in Unocal's 2001 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. The reports are also available on the Unocal web site. You can also obtain this form from the SEC by calling 800-SEC-0330.

Under the terms of the PSCs, Unocal Vietnam, Ltd., and its affiliates, as contractors to PetroVietnam, the Vietnam national oil company, are entitled to varying shares of the oil and gas produced from commercial discoveries.

Updated: May 2002