S-Oil Corp., South Korea\'s third-largest refiner, said Thursday that its net profit tumbled 55.5 percent in the third quarter from a year earlier. Net profit came to 203 billion won (US$192 million) in the July-September period from 456 billion won a year ago, the refiner said in a regulatory filing. Sales fell 4.4 percent to 8.12 trillion won in the period, while operating profit plunged 95 percent to 25 billion won.