The coast guard detected the spill on Thursday evening some 46 kilometres southwest of the island of Utö.
The oil slick, which the coast guard said leaked from a passing vessel, spans over ten kilometres in length. Current estimates put the extent of the spill between 9 and 39 cubic metres.
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“During the night we managed to collect floating oil from the sea and cleanup efforts will continue on Friday,” said Mikko Hirvi, chief of operations at the West Finland Coast Guard.
To combat further environmental damage, officials are using aerial oil spill surveillance to pinpoint smaller oil slicks as the spill breaks up.
Investigators plan to analyse samples from the spill with those taken from fuel tanks of vessels travelling near the accident site.
“We’ll compare spill samples with those taken from ships in the area to determine the source,” Hirvi explained.
The coast guard said it seemed unlikely that any oil would reach the shoreline thanks to removal efforts.