Idemitsu Kosan Co., Japan's third-largest refiner by capacity, plans to approach the Japan Bank for International Cooperation for financing to fund a $5.8 billion refinery in Vietnam.

The Tokyo-based company may fund about 70 percent of the $5.8 billion cost of the Nghi Son refinery with project finance through state-controlled JBIC, Mitsuru Soneda, general manager of the treasury department at Idemitsu, said Tuesday in response to questions at an earnings press briefing.

"The 70 percent figure is not a final number," Soneda said. "The final investment decision hasn't been made yet, so we are not sure how big the investment will be."

Idemitsu and Kuwait Petroleum International Ltd. each have a 35.1 percent stake in the project, while Vietnam Oil & Gas Group, known as PetroVietnam, holds 25.1 percent. Mitsui Chemicals Inc. of Japan has 4.7 percent. The group delayed the final decision on the project to recalculate building costs, putting off its potential start date to 2014.

The investment decision will be made by the end of March, Soneda said. The company hasn't selected an adviser for the project finance, he said.

Idemitsu had ¥128.7 billion in cash and cash equivalents on Dec. 31, according to its earnings statement Tuesday. The company increased its full-year profit forecast by 54 percent to ¥40 billion, it said.