A storage tank containing fuel oil sprung a leak on April 29, flooding the surrounding area but stopping short of the sea.
The leak occurred within a facility owned and managed by petroleum storage company Tankstore on Pulau Busing, which is located off the south-western coast of Singapore, west of Pulau Bukom.
Fuel oil is a heavy oil used for power and heat generation.
The Maritime and Port Authority of Singapore (MPA) said it received a report on the oil spill at about 9.45pm on Saturday.
When contacted, Tankstore informed MPA that one of its tanks had leaked on April 29 at about 12.05pm. The leaked oil was contained within a pit wall around the tank and no oil had spilled into the sea.
MPA said it has not sighted any oil in the waters off Pulau Busing in its daily checks.
Clean-up operations were still in progress as of Tuesday, according to a report by marine fuels publication Platts Bunkerworld.
Tankstore did not respond to queries by press time.
On April 20, an oil tank on Jurong Island had caved in after catching fire. In 2014, a series of ship collisions south of Singapore released hundreds of tonnes of fuel oil into the sea, affecting the beaches and waters of Kusu Island and St John's Island.