Operators of local hotels, restaurants, entertainment places, tour guide firms and souvenir shops have banded together in bringing the lawsuit. They formed an association with about 70 members on Koh Samet and filed their suit with the Criminal Court on Monday.
The oil leaked when being delivered along a pipeline from a tanker vessel to PTTGC's refinery in Rayong on July 27 last year.
The plantiffs accuse the company of failing to properly contain the leaking oil, and of using chemicals that affected the environment to disperse the slick. They argue that the accident greatly damaged tourism on the eastern seaboard island.
The complainants submit that environmental experts estimated the damage at 1 billion baht and that environmental rehabilitation would take a decade.
Sujaree Charoenpol, vice president of the operators' association, said she had negotiated with representatives of PTTGC but had not received a clear response, so the operators decided to file the lawsuit.
Last Friday about 450 fishermen in Rayong sued PTTGC for 400 million baht compensation for damage to their livelihood caused by the oil leak.