press release

Unocal successfully starts Thai oil expansion project

El Segundo, Calif., June 9, 2005 - Unocal Corporation (NYSE: UCL) today said that its Unocal Thailand Limited subsidiary has successfully started up the second oil central processing platform (CPP) at the Platong operating area in the Gulf of Thailand. The Platong Oil CPP 2 was brought online safely and on schedule marking a major milestone for the project's goal of significantly increasing Unocal's current crude oil production in the Gulf of Thailand by the third quarter 2005.

"With the timely platform installation and successful start up on schedule, we are on track to achieve our target of ramping up gross crude oil production to 40,000 barrels per day (b/d) by the third quarter this year, from the current level of 24,000 b/d gross," said Tara Tiradnakorn, Unocal Thailand president. "This production increase significantly adds to Thailand's total indigenous crude oil output and helps the Kingdom reduce its dependence on oil imports."

Unocal Thailand's initial crude oil production from the first phase of the Thai Oil development started at some 3,000 barrels (gross) in July 2001. Oil production from five operating areas - Kaphong, Plamuk, Platong, Surat and Yala - has continued to increase and cumulative production reached 20 million barrels (gross) in January 2005.

The Platong Oil CPP2 is the largest central processing platform ever constructed in Thailand. The CPP was successfully installed at the Platong complex in March after the 13-month construction at CUEL's Laemchabang fabrication yard on Thailand's eastern seaboard.

"The Platong crude oil development not only helps the country meet its rising energy demand but also demonstrates Unocal Thailand's world-class performance in delivering on commitments to the Kingdom of Thailand" said Stephen Green, Unocal's vice president for International Energy Operations. "The 22-month timeframe from project sanction to production startup is another example of the extraordinary capabilities of our Unocal Thailand team."

The Thai oil expansion project is the last of the five major Unocal development projects that were slated to begin production in 2005. So far this year, Unocal has participated in new production from the Mad Dog (Unocal, 15.6% working interest) and K2 (Unocal, 12.5% W.I.) fields in the deepwater Gulf of Mexico, the Moulavi Bazar gas field (Unocal, 100% W.I.) in Bangladesh, and the Central Azeri crude oil export project (Unocal, 10.3% W.I.) in the Caspian Sea.

So far in 2005, Unocal Thailand's gross daily production (Unocal, average 64% W.I.) has averaged approximately 1.280 billion cubic feet of natural gas, 42,000 barrels of condensate, and 24,000 barrels of crude oil.

Unocal Thailand operates 16 operating areas in the Gulf of Thailand on behalf of Mitsui Oil Exploration Co., Ltd., PTT Exploration and Production Public Company Limited, and Amerada Hess (Thailand), Ltd.

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 Asia and North America.

This news release contains forward-looking statements about matters such as production rates and timing and other plans for future operations. Although these statements are based upon Unocal's current expectations and beliefs, they are subject to known and unknown risks and uncertainties that could cause actual results and outcomes to differ materially from those described in, or implied by, the forward-looking statements, including whether the pending merger with Chevron is completed and the effects on Unocal in the event that it is not completed; volatility in commodity prices; Unocal's ability to develop and produce fields in a timely and cost-effective manner; the accuracy of Unocal's estimates and judgments regarding hydrocarbon resources and formations and reservoir performance; operational risks inherent in the exploration, development and production of hydrocarbons; international and domestic political and economic factors; and other factors discussed in Unocal's 2004 Annual Report on Form 10-K and subsequent reports filed or furnished by Unocal with the U.S. Securities and Exchange Commission (SEC).

Copies of Unocal's SEC filings are available from Unocal by calling 800-252-2233 or from the SEC by calling 800-SEC-0330. The reports are also available on the Unocal web site, Unocal undertakes no obligation to update the forward-looking statements in this news release to reflect future events or circumstances. All such statements are expressly qualified by this cautionary statement, which is provided pursuant to the safe harbor provisions of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934.

Updated: June 2005