Three Japanese oil firms said Friday they have reached an accord with the Vietnamese state oil company to jointly explore for oil and gas in an underwater area about 300 km off the coast of Vietnam.

Idemitsu Oil & Gas Co., a unit of Idemitsu Kosan Co.; Nippon Oil Exploration Ltd., an arm of Nippon Oil Corp.; and Teikoku Oil Co. said they signed a production-sharing contract Thursday with Vietnam Oil and Gas Corp., known as Petrovietnam, for two offshore blocks southeast of Ho Chi Minh City.

The interest in both blocks is owned 35 percent by Idemitsu, 35 percent by Nippon Oil and 30 percent by Teikoku. The trio did not disclose how much they paid Petrovietnam for the exploration rights.

The two blocks, 1,570 sq. km in total, are at a depth of between 100 meters and 200 meters. Several oil and gas fields are located nearby, according to the companies.

The three firms will explore the area by October 2007.