press release

Unocal announces deepwater discovery at Puma

Sugar Land, Texas, Jan. 13, 2004 - Unocal Corporation (NYSE: UCL) today said that the exploratory well in the Puma prospect, operated by BP (NYSE: BP [ADR]) in Green Canyon block 823, is a significant discovery in a hydrocarbon-rich area near existing developments.

Drilled to a depth of 19,034 feet, the Puma discovery well encountered approximately 500 net feet of oil pay in Miocene-age reservoirs. Two subsequent sidetrack bores encountered oil in reservoir intervals of a similar age. Initial indications of reservoir productivity are encouraging, based on preliminary analysis of sidewall cores and fluid samples taken from the well.

"The Puma discovery's proximity to Mad Dog allows the option of either a stand-alone development or a tie-back, depending on future appraisal results," said Mike Bell, vice president for Unocal's Deepwater USA unit. "Puma is structurally complex and will require additional seismic data and appraisal drilling to determine the size of the field.

"The confirmation of lower and middle Miocene sands at Puma further enhances prospectivity in southeast Green Canyon, where we are currently drilling the Myrtle Beach prospect. We are very pleased with what these results mean for the value of our prospect inventory in this area."

Unocal said that following the Myrtle Beach well, the Discoverer Spirit drillship will move to Alaminos Canyon 859 to drill the Tobago wildcat. Tobago will be testing the structure directly between the Trident and Great White oil discoveries.

In addition to Myrtle Beach and Tobago, Unocal's deepwater Gulf of Mexico drilling plan for 2004 includes an appraisal well at the St. Malo discovery in Walker Ridge 678; La Jolla, a structure directly south of and saddle-separated from St. Malo; and Sardinia, a lower Tertiary test in Keathley Canyon 681.

"Our 2004 program is focused on drilling prospects that are on trend with recent Unocal or industry discoveries," Bell said. "We have the ability to execute deals that allow the company to manage dry hole exposure for the program."

The BP-operated Puma well lies immediately to the west of the Mad Dog development (Green Canyon 826), where production startup is planned for early 2005.

The Puma well spud on Aug. 14 and was drilled in 4,130 feet of water. As operator, BP holds a 51.66-percent working interest in this prospect. Unocal holds 15 percent, and the remaining 33.34 percent is held by BHP Billiton Ltd. (NYSE: BHP [ADR]).

Elsewhere, Unocal has moved the Discoverer Spirit off the Hawkes prospect in Mississippi Canyon block 508. Unocal will take a pre-tax charge to fourth quarter 2003 earnings of approximately $8 million for this well.

This news release contains certain forward-looking statements about Unocal's assessment of the quality of the hydrocarbon formation. 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). Copies of the company'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 this form from the SEC by calling 800-SEC-0330.

Updated: January 2004