The council said the estimate covered the short-term impact as the accident occurred in the low season for tourists visiting the island, chairman Piyaman Techapaibul said on Thursday.
The oil slick has caused damage to Ao Phrao beach on western Samet since Sunday night and crews are cleaning up the spill. Other beaches on the other side of the island are not affected.
Samet is the main tourist destination for visitors to Rayong. The eastern province made 16 billion baht in revenue from tourism last year, 40% of that amount coming from the island, according to the Rayong Tourist Association. Samet has about 40 hotels catering to tourists.
Meanwhile, the Koh Samui Tourist Association has expressed concern to the council about possible problems for tourists to the island in Surat Thani province due to new oil drilling schemes possibly to be undertaken in the Gulf of Thailand near the island.
Mr Piyaman said council members are discussing whether to file complaints to the House Committee on Tourism and Environment.