Three Japanese firms led by project operator Idemitsu Kosan Co said on Thursday they have found oil and gas in an offshore exploration well in southern Vietnam, as Japan's energy sector steps up exploration activity in Southeast Asia.
The companies did not give detailed figures on reserves, saying they would make evaluations later.
The discovery was in the Dai Nga structure in Blocks 05-1b and 05-1c, about 300 km (188 miles) southeast of Ho Chi Minh City.
A wholly owned Idemitsu unit and JX Nippon Oil & Gas Exploration, part of JX Holdings, each holds a 35 percent stake in the blocks, while an Inpex Corp unit has the rest.
The three firms entered into a production sharing contract with Petrovietnam in 2004.