Unocal Corporation said its Southwest Vietnam Exploration & Production, Ltd., subsidiary signed a production-sharing agreement for petroleum exploration with Petrovietnam for Block 52/97. The block is in the northern portion of the Malay Basin in approximately 195 – 230 feet of water and located approximately 330 miles west-southwest of Vung Tau, Vietnam and 160 mile east of Songkhla, Thailand. It covers more than 500,000 acres. Block 52/97, adjacent to Unocal's Block B exploration area, had been part of the offshore overlap area between Vietnam and Thailand. The two countries agreed on the delimitation of their shared continental shelf in December 1997, making the strip available for exploration. Block B was awarded to Unocal and its coventurers in May 1996; the adjacent block 48/95 in September 1998. The addition of block 52/97 brings Unocal's total exploration area to approximately 4.15 million acres. Unocal Thailand has a 16-percent interest in the adjacent Blocks 14, 15 and 16 on the Thailand side of the shared continental shelf. Unocal discovered gas with its first exploration well on the Kim Long prospect on Block B in late 1997. Two drill stem tests on the well yielded a combined rate of 52.9 million cubic feet per day (mmcfd) of gas. Unocal conducted a 3-D seismic acquisition program on Block B and Block 52/97 in 1998. Unocal has a 45-percent working interest and is operator of Block B. Unocal Southwest Vietnam Exploration & Production, Ltd. has a 70-percent working interest in Block 52/97 and serves as operator, while Moeco Southwest Vietnam Petroleum Co., Ltd., a subsidiary of Mitsui Oil Exploration Co., Ltd., holds the remaining 30-percent interest. Petrovietnam has an option to retain its 30-percent working interest at the time of a commercial gas discovery. If exercised, Unocal's and Moeco's interests would be reduced proportionately.