GS Caltex Co., South Korea’s second-largest oil refinery, said Sunday that it has started commercial operation of its fourth heavy oil processing plant.

GS Caltex spent 1.3 trillion won ($1.2 billion) to build the plant in Yeosu, 455 kilometers south of Seoul, that converts heavy oil into transportation fuels like gasoline and diesel, the company said in a statement.

The plant processes 53,000 barrels of heavy oil per day, boosting the company’s daily heavy oil processing capacity to 268,000 barrels and making the refiner the country’s largest processor of heavy oil, GS Caltex said.

GS Caltex’s ratio of heavy oil processing capacity to total refining facilities was increased to 34.6 percent from 27.7 percent, the company said.

Unlisted GS Caltex is an equal joint venture between GS Holdings Corp. of South Korea and Chevron Corp., the second-largest U.S. oil company. (Yonhap News)