Black Stone Minerals Company, L.P. Agrees to Buy Pure Resources, L.P. Upper Gulf Coast Fee Mineral and Royalty Assets for $192.4 Million.

Energy Editors/Business Editors

HOUSTON--(BUSINESS WIRE)--March 11, 2004

Acquisition adds significant fee minerals, reserves and production

in core areas for Black Stone

Black Stone Minerals Company, L.P (Black Stone) announced that it has entered into an agreement to buy all of the Upper Gulf Coast producing and non-producing fee mineral and royalty assets and some limited associated working interest properties of Pure Resources L.P., a wholly owned subsidiary of the UNOCAL Corporation (NYSE:UCL) for approximately $192.4 million effective Oct. 1, 2003.

The properties are located in ten states -- ranging from Mississippi, Texas, Alabama, Louisiana, Oklahoma, Florida, Arkansas, Pennsylvania, Michigan and New York -- comprising approximately 5.6 million gross acres, or 3.3 million net acres, and include royalty and overriding royalty interests in approximately 1100 wells with net daily production of approximately 13.5 million cubic feet per day on a gas equivalent basis.

The transaction has been approved by the board of directors of both companies and is expected to close on or before the end of June 2004. The purchase price will be adjusted to reflect the effective date of Oct. 1, 2003.

"This acquisition is a major step forward for Black Stone," said Thomas L. Carter, Jr., president of Black Stone. "We like the Pure Resources minerals for their geographic diversity, solid production base and acreage position. They compliment our existing portfolio of assets and are consistent with the business model that we have established that is intended to earn our investors and limited partners superior returns. We also look forward to working creatively with the industry to further the leasing, exploration and development of Pure's extensive unleased acreage."

Black Stone is one of the largest privately owned mineral companies in the United States. Along with its limited partners and other investors, Black Stone now owns interests in approximately 13 million gross mineral and royalty acres in virtually every significant onshore exploration basin in the lower 48 states, with interests in approximately 15,000 wells producing in excess of 3.1 million barrels of oil equivalent per year.

Pure Resources, L.P., a wholly owned subsidiary of the UNOCAL Corporation, is headquartered in Midland, Texas, and is an independent energy company engaged in the acquisition, development, exploration and production of natural gas and crude oil. The company holds interests in developed and undeveloped oil and gas properties in the Permian Basin of West Texas, San Juan Basin in New Mexico and Colorado and the Upper Gulf Coast region of Texas and Louisiana. More information about Pure Resources, L.P., or UNOCAL may be found at the company's Web site, www.unocal.com.

Safe-Harbor Statement -- Except for the historical information contained herein, the matters set forth in this news release are "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. The company intends that all such statements be subject to the "safe-harbor" provisions of those Acts. Many important risks, factors and conditions may cause the company's actual results to differ materially from those discussed in any such forward-looking statement. These risks include, but are not limited to, estimates of reserves, estimates of production, future commodity prices, exchange rates, interest rates, geological and political risks, drilling risks, product demand, transportation restrictions, the ability of Pure to obtain additional or alternative capital, and other risks and uncertainties described in the company's filings with the Securities and Exchange Commission (SEC). The historical results achieved by the company are not necessarily indicative of its future prospects. The company undertakes no obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

Cautionary Notes to Investors -- The Securities and Exchange Commission (SEC) 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. Investors are urged to also consider closely the disclosure in Pure's Form 10-K for the fiscal year ended Dec. 31, 2003, available from the company by calling 310-726-7665. This form also can be obtained from the SEC at www.sec.gov.