April 27 (Reuters) - South Korea's S-Oil Corp said on Wednesday that regional refining margins in the second quarter are expected to stay firm supported by seasonal demand and easing pandemic restrictions amid sustained global supply tightness.

S-Oil is the country's third-largest refiner, whose main shareholder is Saudi Aramco

(Reporting by Byungwook Kim and Heekyong Yang; Editing by Jacqueline Wong)