New York's main contract, light sweet crude for delivery in December, fell 68 cents to $91.51 per barrel in the afternoon.

Brent North Sea crude for December delivery shed 53 cents to $109.01.

Greek Prime Minister George Papandreou's call for a national vote on the rescue package hammered out last week by European leaders sent shock waves through crude markets, Phillip Futures said in a report.

A "possible referendum in Greece on its debt bailout revived concerns about the eurozone... Papandreou's unexpected move had sent the euro, equities and oil prices sharply lower," it said.

Papandreou's decision to hold a confidence vote on Friday followed by a referendum sent European bourses tumbling Tuesday and earned harsh rebukes from European Union countries including France and Britain.

British finance minister George Osborne said there was "no doubt" that Greece's shock decision has "added to the instability and uncertainty" in the eurozone.

Meanwhile, "weak" economic data out of China, Britain and the United States "reinforced concerns about slowing economies curbing oil demand", Phillip Futures' report said.

Manufacturing activity in the US and China -- the world's largest oil and energy consumers respectively -- expanded at a slower pace last month than in September.

Britain's economy grew faster than expected in the third quarter, official data showed on Tuesday, but could come unstuck owing to high inflation, government cutbacks and the eurozone debt crisis.