New York's main contract, light sweet crude for delivery in December, fell 74 cents to $91.45 per barrel.

Brent North Sea crude for December delivery shed 59 cents to $108.95.

Greek Prime Minister George Papandreou's call for a referendum on a debt rescue package hammered out just days ago 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 on the debt deal prompted European bourses to dive overnight, and earned harsh rebukes from European Union countries including France and Britain.

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

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

Data released on Tuesday showed manufacturing activity in the US and China -- the world's largest oil and energy consumers respectively -- expanding 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 faces coming unstuck owing to high inflation, government cutbacks and the eurozone debt crisis.