SINGAPORE - The police have seen a rise in the theft of marine oil in Singapore waters.

The diesel is first stolen by Indonesian crew members from their own vessels, then sold to another vessel at almost half its usual price.

Crew from the buyer vessels, also Indonesians, then act as a middleman and sell the oil to another vessel, outside of Singapore waters, at a slightly higher price that is still below market value.

In 2013, 6,000 litres of oil were exchanged illegally.

This year, up to July, 60,000 litres of oil changed hands, said the Police Coast Guard's Deputy Commander (Special Duties) Lim Kim Tak. The 10-fold jump was mostly due to one incident involving 50,000 litres of oil, he said.

He spoke of the increasing trend at a press conference at the coast guard's Brani base in southern Singapore. Stealing marine oil may fall under the offence of criminal breach of trust, which for offenders carries a maximum jail term of seven years, a fine, or both.

Those who buy the stolen oil may be found guilty of dishonestly receiving stolen property, which may mean up to five years in jail and a fine.