press release

Unocal's Northrock unit announces successful offer for Tethys shares

Calgary, Alberta, July 17, 2001 -- Unocal Corporation's (NYSE:UCL) Northrock Resources Ltd. subsidiary today said that it had successfully completed the terms of its offer for all of the common shares of Tethys Energy Inc. (TO: TET). Northrock has taken up all of the shares deposited under the bid. Shareholders of Tethys will receive C$4.25 (US$2.76) for each Tethys common share deposited.

Northrock has directed the depositary for the bid, Computershare Trust Company of Canada, to mail payment for the Tethys common shares deposited under the bid in the next three days.

Northrock said that 31 million Tethys common shares, representing approximately 96 percent of the Tethys common shares, were tendered. Northrock intends to exercise its statutory right to acquire the additional Tethys common shares not tendered to the bid for the same consideration paid pursuant to the offer.

Based on an independent reserve report and successful exploration and development activity in 2001, Tethys has proved reserves (U.S. basis) of 12 million barrels-of-oil equivalent (BOE) on a 6:1 net basis. More than 60 percent of the reserves are liquids-rich natural gas.

Tethys' current production is 4,600 barrels-of-oil equivalent (6:1 net basis) per day, including 16 million cubic feet per day of natural gas production.

This news release contains certain forward-looking statements about expected production, reserves and business transactions. 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 2000 Form 10-K and other reports filed with the U.S. Securities and Exchange Commission. Unocal undertakes no obligation to update the information in this news release.

Investors are urged to consider closely the disclosure in Unocal's 2000 Form 10-K and other reports. 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.

Updated: July 2001