On Wednesday, Brent crude fell for a fourth day to depict the longest losing streak since September, on worries that renewed euro zone debt woes and weak economic data from China and the United States may hurt global recovery and minimize oil demand.
Global markets were pummeled by a shock call by Greek Prime Minister George Papandreou for a vote on the currency bloc's bailout plan besides throwing into question the survival of crucial efforts to contain the euro zone's sovereign debt crisis.
On Tuesday, the gloomy outlook was compounded by data revealing slower manufacturing activity in China and the United States, the world's largest oil consumers.
Brent crude was down 26 cents, or 0.24 percent, at $109.28 a barrel by 0612 GMT (2:12 a.m. EDT) while U.S. crude on the New York Mercantile Exchange was down 26 cents, or 0.28 percent, to $91.93 a barrel.
"Greece's referendum plan has introduced a new level of uncertainty over the EU debt crisis," said Nader Naeimi, a strategist at AMP Capital Investors Ltd in Sydney.
"And you have worries about a weakening China, a really heavy consumer of commodities."
The Greek government faced possible collapse as ruling party lawmakers demanded that Papandreou resign for throwing the nation's euro membership into jeopardy.
"It was a very sudden decision and there is a risk that people in Greece will reject the bailout plan," Yusuke Seta, a commodity sales manager at Newedge Japan, said.
"Brent could fall further to $100 because we are anxious over where the world economy is going," Seta said. "The situation is very vulnerable."