press release

Unocal subsidiary purchases Amoco Thailand Petroleum Co., Ltd. shares

Bangkok, Sept. 25, 2002 - Unocal Thailand, Ltd. today said it had reached agreement with BP America Production Co. for an affiliated company to purchase all of the shares of Amoco Thailand Petroleum LLC. Amoco Thailand Petroleum is operator and 50-percent owner of the concession covering Blocks 5 and 6 in the Thai-Cambodia Overlapping Claims Area (OCA) in the Gulf of Thailand.

Terms of the purchase were not disclosed.

Unocal Thailand is a wholly owned subsidiary of Unocal Corporation (NYSE: UCL). Idemitsu Oil & Gas Co., Ltd. holds the remaining 50-percent working interest in Blocks 5 and 6.

Blocks 5 and 6 cover a current combined area of 10,155 square kilometers (3,900 square miles) and have been held under a moratorium since the early 1970s pending resolution of the OCA. In June 2001 the governments of Thailand and Cambodia signed a memorandum of understanding (MOU) to provide a framework for the joint discussions. Under the terms of the MOU, Blocks 5 and 6 will be delimited by a boundary line into separate Thai and Cambodian parts.

"Although the final resolution of the OCA will take some additional time to complete, purchasing Amoco Thailand shares shows Unocal's commitment to long-term growth in Thailand," said Randy Howard, president of Unocal Thailand. "These additional blocks will complement the company's existing blocks in the OCA (10, 11, and parts of 12 and 13). We look forward to working with the governments of Thailand and Cambodia to reach a speedy resolution of all remaining issues."

Once the boundary issues are resolved, Unocal Thailand expects to conduct a 3D seismic survey on the blocks in the first year, followed by exploration drilling in the following years.

Unocal Thailand was the first gas producer in the Gulf of Thailand and is operator for a current contracted volume of gas of more than 1 billion cubic feet per day. Recently the company increased oil production from the northern area of its existing concessions.

About Unocal

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, Asia, Latin America, and the North Sea. 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 exploration activities. 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.

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.

Updated: September 2002