South Korea\'s corporate watchdog said Thursday that it has decided to fine the nation\'s four major oil refiners a combined 434.8 billion won (US$399 million) for colluding in their operation of gas stations. The four refiners SK Energy Co., GS Caltex Corp., Hyundai Oilbank Corp. and S-Oil Corp. were found to have been avoiding selling their products to gas stations held by their competitors in order to guarantee their stable market shares without fierce competition, the Fair Trade Commission (FTC) said in a press release. SK Energy, owned by SK Innovation Co., has to pay 138 billion won in fines while GS Caltex, Hyundai Oilbank and S-Oil were fined 177.2 billion won, 74.4 billion won and 45.2 billion won, respectively, the FTC said. The FTC added that it will refer SK Innovation, GS Caltex and Hyundai Oilbank to the prosecution for investigation. \"In their meeting in March 2000, officials of the four refiners agreed to respect the rights of former exclusive oil suppliers to gas stations and refrained from supplying their products to even such gas stations with ties with a particular brand in the past,\" the FTC said. Such a deal hampered competition among refiners in setting supply prices for gas stations and eventually prevented price cuts that might have been enjoyed by consumers, the FTC noted. Oil refiners, however, denied the charges, with some of them reportedly planning to appeal the decision. \"Competition was under way even during the period mentioned by the FTC when the alleged collusion was taking place,\" a refiner official said on the condition of anonymity, rebutting the watchdog\'s argument. The relations between oil refiners and gas stations have been under close scrutiny as suspicions have mounted that shady deals might be preventing price reductions at the pump even in the case of downturns of crude costs in the international market. The oil industry is one of the key areas that the government has been keeping an eye on for such irregularities as sky-high gasoline and diesel prices are being blamed for driving up inflationary pressure. With the government\'s probe into the oil industry under way, major refiners cut gasoline and diesel prices in April by 100 won per liter to help contain inflation. But the move has apparently failed to make a dent as oil prices are showing few signs of going down. The FTC expected that its latest decision will encourage competition among refiners and eventually lead to price cuts, helping consumers enjoy cheaper prices down the road.