SK Innovation Co., the holding company of South Korea's biggest refiner, said Friday that its net income rose 50.8 percent in the fourth quarter from a year earlier thanks to a strong won.

Net profit came to 228 billion won (US$209.5 million) in the October-December period, compared with 151 billion won a year ago, SK Innovation said in a regulatory filing.

Sales rose 1.4 percent on-year to 17.15 trillion won, but operating profit fell 44.1 percent to 202 billion won, the company said.

"The South Korean won's appreciation against the U.S. dollar contributed to the good fourth-quarter performance, cutting the expense of buying crude," Yoo Jung-min, a spokesman at SK Innovation said.

For all of 2012, SK Innovation posted 1.15 trillion won in net profit, down 63.9 percent from a year ago, due to its decreased refining margin. Sales rose 7.3 percent to 73.3 trillion won, but operating profit fell 43 percent to 1.69 trillion won due to the sluggish performance in the petroleum and lubricant business.

SK Energy Co., the refining unit of SK Innovation, logged 13.3 trillion won in sales and 78.5 billion won in operating profit in the fourth quarter. Its operating profit fell 55 percent in the quarter from a year ago due to weak refining margin.

SK Lubricants Co., a subsidiary of the holding company, also posted 28.6 billion won in operating loss in the fourth quarter due to the contraction in both sales and margin for base oil.

SK Global Chemical Co., another SK Innovation's petrochemical unit, however, staged a good performance in the fourth quarter, posting 137.4 billion won in operating profit compared with 92.2 billion won a year ago.

Shares of SK Innovation fell 2.04 percent to 168,000 won as of 11:29 a.m. on the Seoul bourse. (Yonhap News)