press release

Unocal outlines plan to double its Thailand oil production to 40,000 b/d

El Segundo, Calif., Sept. 2, 2003 -- Unocal Corporation (NYSE: UCL) today said its Unocal Thailand Limited subsidiary is seeking Thailand government approval for the second phase of its oil development in Thailand, which would double current gross oil production from the offshore Gulf of Thailand Yala and Plamuk fields to 40,000 barrels per day.

"Since we started oil production in late 2001, estimated oil resources in place have increased significantly," said Randy Howard, president of Unocal Thailand. "Successful delineation wells, combined with continued positive production performance from our Phase 1 oil development, have contributed to our decision to move forward with the second phase development."

The company said the resource potential has more than doubled since commencement of Phase 1 and is now approaching 100 million barrels of oil. Unocal expects to be able to add to the resource base in the future through additional delineation drilling and through improved recovery efficiencies.

"Continued growth in domestic oil resource potential and production is an important objective for the Kingdom of Thailand, and this plan provides significant near-term contribution to that goal," Howard said.

The first phase of Unocal Thailand's oil development from the Platong, Yala, Surat, and Plamuk fields is currently producing more than 20,000 barrels of oil. The Phase 2 development will include facilities and wells that will bring oil rates to 40,000 barrels per day. Current plans are to have the new facilities installed by mid-2005, with start-up commencing soon thereafter.

Unocal Thailand is the operator and holds 71.25-percent working interest in the Yala, Plamuk, and Surat fields. Its co-venturers are Mitsui Oil Exploration Co., Ltd. (23.75%) and PTT Exploration and Production Public Company Limited (5%). Unocal Thailand also operates the Platong and Kaphong fields, and holds a 70-percent working interest in those fields, while Mitsui Oil Exploration holds the remaining 30-percent stake.

Unocal's global growth profile

Charles R. Williamson, Unocal's chairman and chief executive officer, said, "Approval of Phase 2 of our Thailand oil development is another positive step forward for Unocal and adds to our robust inventory of major development projects. The Phase 2 oil project in Thailand is particularly attractive because we can get our first production in less than two years from our development decision. These major development projects give us excellent line of sight for what we think will be competitive and profitable production growth over the next five to ten years."

Williamson added that the first phase of the West Seno deepwater project in Indonesia recently began production. By the end of 2005, other new production is expected to come from West Seno Phase 2; Moulavi Bazar in Bangladesh; Xihu Trough in the East China Sea; Phase 1 of the Azerbaijan International Operating Company (AIOC) crude oil development in the Caspian Sea; Mad Dog and K2 in the deepwater Gulf of Mexico; and South Kenai gas in Alaska.

"We also have a large and growing inventory of discoveries which we will be progressing to approval for development beyond 2005," Williamson said. "Unocal has a large untapped gas position in Asia that will provide longer term growth for the company as new markets develop."

About Unocal Corporation and Unocal Thailand

Unocal Thailand is a wholly owned subsidiary of Unocal Corporation, one of the world's leading independent natural gas and crude oil exploration and production companies. Unocal's principal oil and gas activities are in North America and Asia.

This news release contains certain forward-looking statements about Unocal's expected production rates, resource potential, future development plans and capital expenditures. Resource potential is a speculative estimate (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 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).

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 "resource potential," that the SEC's guidelines strictly prohibit Unocal from including in its filings with the SEC.

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: September 2003