In the first quarter of last year, the refiner reported an operating income of 845 billion won.

S-Oil Corp., the No. 3 refiner here, is predicted to have racked up 391 billion won in operating income on sales of 4.96 trillion won in the first quarter.

The first-quarter operating income of GS-Caltex Corp., the second-largest in the sector, is estimated at 661 billion won, sharply up from 316 billion won a year earlier.

The refining margin stood at an average of $6.9 per barrel and $6.7 per barrel, respectively, in January and February. In March, the comparable figure was almost the same.

Usually, a refiner can generate a profit with a refining margin of $4 or more per barrel.

Refining margins will stay firm this year on the back of solid demand for oil from Asian countries, and demand for power generation will also remain solid.

US refiners are expected to conduct large-scale maintenance work this year, according to Lee Dong-wook, an analyst at Kiwoom Securities. "Local players will benefit from firm demand amid tight supply," said Lee.

Refiners in South Korea racked up record earnings last year largely due to improved cracking margins, inventory gains and solid demand for petrochemical products.

The country's four major oil refiners -- SK Innovation, GS Caltex, S-Oil and Hyundai Oilbank Co. -- logged a combined operating income of 8.03 trillion won last year, an all-time high figure.

Industry leader SK Innovation already posted a record operating income of 3.23 trillion won last year, while No. 2 GS Caltex logged an operating income of 2.14 trillion won. (Yonhap)