An oil refinery project involving Idemitsu Kosan Co., Mitsui Chemicals Inc. and state-run oil companies of Vietnam and Kuwait has begun commercial operations, Idemitsu Kosan said Tuesday.

The Nghi Son Refinery and Petrochemical Complex, Vietnam's second refinery, has a daily production capacity of 200,000 barrels. The two Japanese firms, Vietnam Oil and Gas Group and Kuwait Petroleum Europe B.V., have invested $9 billion.

Idemitsu and Kuwait Petroleum Europe each have a 35.1 percent stake in the refinery operation, with Vietnam oil holding a 25.1 percent share and Mitsui 4.7 percent.

Refined oil at the complex is for domestic consumption. Its petrochemical products are exported to other markets.

Idemitsu is keen to expand its business in Southeast Asia as oil demand continues to decline in its home market. The company provides engineers and technological assistance for the project.

"We are giving high priority to Southeast Asia. We want to utilize the experience in Vietnam for future business development," Idemitsu's executive vice president, Takashi Matsushita, said during a news conference.

The Dung Quat Oil Refinery, Vietnam's first oil refining facility, has a daily capacity of 148,000 barrels.