Oil prices fell on renewed economic concerns, putting Brent on track for about a 10% drop this month and its biggest quarterly decline in five quarters.
Data showed China's manufacturing sector contracted for an update third consecutive month in September, adding to doubts about Europe's ability to solve its debt crisis nudged investors to sell riskier assets such as equities and commodities.
The gloomy economic outlook and weak demand in the United States have dragged markets down this quarter, while the expected return of oil exports from Libya, cut off by the civil war added a bearish spin this month.
Demand is very poor in the Atlantic basin, prices are high, unemployment is high, so we'd need to get greater confidence and a change in the employment picture to get a strong rebound, said Olivier Jakob, an analyst at Petromatrix in Zug, Switzerland.
In London, ICE Brent for November delivery fell 48 cents to 103.47 dollars a barrel, after hitting an early low of 101.78.
US November crude dropped 1.58 to 80.56 dollars, having fallen earlier to a session low of 80.04.
Brent crude has fallen 9.9% this month, its steepest drop for a month since May 2010. For the quarter, it is down 8%, the weakest performance since the second quarter of 2010.
US crude has declined 9.3% this month, its biggest drop since May this year. For the quarter, it has dropped 15.6%, its worst performance since the last quarter of 2008.