SEOUL (Reuters) - South Korea's two major refiners are considering legal action to recover losses tied to the collapse of the world's largest marine fuel supplier, Denmark's OW Bunker, spokespeople of the refiners said on Thursday.

OW Bunker filed for bankruptcy last Friday after an alleged fraud at a Singapore subsidiary cost it at least US$125 million and banks refused to provide new credit lines, throwing the world's ship fuel market in turmoil.

Oil firms have this week commenced legal action against the Singapore units of OW Bunker, with the arrest of a ship fuel delivery barge Laguna on Wednesday and claims filed in Singapore totalling more than $5 million.

"We are considering all possible legal actions...We don't have exact schedules over legal actions, though," a spokeswoman at SK Innovation Co Ltd, which fully owns South Korea's largest refiner SK Energy, told Reuters by phone.

She declined to comment on the size of the refiner's losses.

Another South Korean refiner GS Caltex Corp, a joint venture between GS Holdings and Chevron Corp, is also considering legal action, a spokesman said, without elaborating. He also declined to disclose the losses.

South Korea exports around 700,000 tonnes of bunker fuel oil a month on average, and OW traded and sold around 100,000-150,000 tonnes a month, according to traders estimates.