press release

Unocal unit agrees to sell fee mineral interests to Black Stone Minerals

Midland, Texas, March 11, 2004 -- Unocal Corporation (NYSE: UCL) said today its Pure Resources subsidiary has agreed to sell certain fee minerals interests it holds in several states to Black Stone Minerals Company, LP for approximately $190 million in cash. The purchase price will be adjusted to reflect the effective date of Oct. 1, 2003. The sale is expected to close by the end of the second quarter 2004.

The transaction involves Pure Resources' royalty interests, overriding royalty interests, minor working interests, and subsurface mineral rights on approximately 3.3 million net acres, primarily in Texas, Louisiana, Mississippi, Arkansas and Alabama.

The assets being sold account for approximately 2,250 barrels of oil equivalent (BOE) per day of production. The production is included in Unocal's reported operating data.

"This sale will allow Pure Resources to focus exclusively on its core exploration and production program," said Tony Best, president of Pure Resources. Pure Resources operates primarily in the Permian Basin of West Texas, in south and east Texas and in New Mexico's San Juan Basin.

Unocal expects to record a gain on the sale in the second quarter 2004.

About Black Stone Minerals

Located in Houston, Black Stone Minerals Company and its related financial affiliates and limited partners are one of the largest private royalty and fee mineral owners in the United States. Prior to the acquisition of the Pure Resources interests, Black Stone's ownership includes interests in more than 13,000 oil and gas wells and in excess of 7.5 million gross acres located in more than 40 states. Additional information on Black Stone is available on the company's web site at www.bsmc.cc.

About Unocal

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. Pure Resources is a wholly owned subsidiary of Unocal Corporation, headquartered in Midland, Texas. For additional information about Unocal and its operations, visit the company's web site at www.unocal.com.

This news release contains certain forward-looking statements about the success of future business transactions and the expected earnings impact from the sale of assets. 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 2003 Annual Report on Form 10-K (SEC File No. 1-8483) and other reports filed with the U.S. Securities and Exchange Commission. Unocal undertakes no obligation to update the information in this news release.

Copies of the Unocal'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 filings from the SEC by calling 800-SEC-0330.

Updated: March 2004