S-Oil Corp., South Korea's third-largest refiner, said Monday that it logged a loss in the third quarter of the year, hit by a slump in its refining business.

The net loss came in at 46.7 billion won ($41.3 million) in the July-September period, narrowing from a loss of 109 billion won a year earlier, S-Oil said in a regulatory filing.

Sales declined 39 percent on-year to 4.43 trillion won, while operating profit swung to a profit of 12.4 billion won from an operating loss of 38.3 billion won, the firm said.

"A slump in oil prices has led to a drop in product prices, and sales declined due to regular maintenance works," the company said.

Its refinery business logged 3.49 trillion won in sales during the third quarter but suffered a loss of 171 billion won.

S-Oil said its petrochemicals unit logged an operating income of 88 billion won on sales of 610 billion won.

Its lubricant segment posted an operating income of 95.6 billion won on sales of 329 billion won, S-Oil said.

Shares of S-Oil were trading at 70,400 won on the Seoul bourse as of 10:35 a.m., up 1.29 percent from the previous session's close. The third-quarter earnings were released after the market opened. (Yonhap)