press release

Unocal announces additional open market purchases of Tethys stock by its Northrock Resources subsidiary

Calgary, Alberta, June 18, 2001 -- Unocal Corporation (NYSE:UCL) said its Northrock Resources Ltd. subsidiary today purchased 430,300 common shares of Tethys Energy Inc. (TO:TET) at an average price of C$4.23 (US$2.76) per share for an aggregate purchase price of approximately C$1.8 million (US$1.2 million) on the open market. The highest price paid was C$4.23 (US$2.76) per Tethys common share.

The Tethys common shares purchased today, combined with purchases on June 15, 2001, of 203,500 common shares, represent approximately 2.1 percent of the outstanding number of Tethys shares. To date, the average price paid for purchases of Tethys common shares by Northrock was C$4.22 (US$2.76) per share.

Northrock has mailed to all holders of common shares of Tethys an offer and bid circular dated June 8, 2001. Pursuant to the offer, Northrock offers to purchase all of the issued and outstanding common shares of Tethys for C$4.25 (US$2.77) cash. It is intended that the Tethys common shares acquired today by Northrock will be included in determining whether the 66-2/3 percent minimum acceptance condition set out in the offer has been fulfilled.

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 operations are located in North America (Gulf of Mexico region, Alaska and Canada) and in Asia (Thailand, Indonesia, Myanmar and Bangladesh). The company is also pursuing exploration programs in West Africa and Brazil.

Updated: June 2001