Two Singapore-registered bunker tankers collided near St John's Island resulting in a 200-tonne oil spill, maritime officials said on Friday.
No one was injured in the crash on Thursday and most of the spill was cleaned up, the Maritime and Port Authority (MPA) said.
The Seafalcon and the Frontek were sailing from opposite directions and rammed into each other 500 miles south of the island in Singapore's waters, the MPA said.
The tankers operate as "floating fuel stations" that refuel ships sailing to and from other countries.
The collision damaged one of the Seafalcon's 10 tanks. The Frontek's bow was damaged, but no oil spilled from it.
The MPA had dispatched five-anti-pollution craft to the scene. The clean-up continued late into the night.
As a precaution, authorities have placed an oil boom around the vessel. The remaining oil carried by the Seafalcon was transferred to another tanker.
The incident did not affect port operation and is under investigation, the MPA said.