Oil prices slumped Friday on renewed global economic worries, pushing back Brent more than 10 percent this month for its biggest quarterly decline in five quarters.
U.S. crude futures fared even worse, posting their weakest quarterly performance since the financial crisis of 2008 as awobbly economy sparked more demand worries.
Crude futures fell with a broad array of commodities, led by copper, which with U.S. equities tumbled to its worstquarter since 2008.
In London, ICE crude for November delivery settled at $102.76 a barrel, dropping $1.19, or 1.14 percent, aftertouching a session low of $101.78.
For the quarter, Brent crude fell $9.72, or 8.64 percent, the biggest percentage loss since the second quarter of 2010.
For the month, front-month Brent dropped $12.09, or 10.53 percent, the biggest monthly decline since May 2010.
U.S. November crude settled at $79.20 a barrel, falling $2.94, after dropping to an intraday low of $78.77.
For the quarter, U.S. crude fell $16.22, or 17 percent, the biggest percentage loss since the fourth quarter of 2008. For the month, it dropped $9.61, or 10.82 percent, the biggest monthly decline since May 2010.
Brent's premium against U.S. crude rose back to $23.56, after dropping to $21.81 on Thursday.CHINA DATA ADDS TO CLOUDY OUTLOOK
The day's sell-off began after data showed that China's manufacturing sector contracted for a third consecutive month in September, adding to doubts about Europe's ability to solve its debt crisis.
That drove investors to sell riskier assets such as equities and commodities. Trading was volatile on quarter-end booksquaring, traders said.
The dollar rose while the euro sank, curbing risk sentiment across many commodities markets.
A 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.
``Declines in the stock market and the euro prompted much of today's weakness amidst reduced risk appetite,'' said Jim Ritterbusch, president at Ritterbusch & Associates in Galena, Illinois.
Trading in Brent was more hectic than U.S. crude, reaching 701,000 contracts as of 3:45 p.m. EDT (1945 GMT), which was 33 percent above its 30-day average.
U.S. crude volume hit nearly 599,000 contracts, down 5.3 percent from its 30-day average.
OPEC, LIBYA ADDING TO GLOBAL SUPPLIES
Supply from all 12 members of the Organization of the Petroleum Exporting Countries is forecast to average 30.25 million barrels a day this month, up from 30.15 million in August, according to a Reuters survey.
Libya's output has begun to recover after falling to almost nothing in the civil war, the survey found. The country exported one small crude cargo on Sept. 25 and is reported to be sending some oil to refineries.
``If the current positive reports from Libya are confirmed, then domestic production could reach 1.3 million barrels per day by the end of next year,'' JP Morgan said in a note.
``On an annual average, this would lead to exports of around 0.6 mbd of light sweet crude, which together with rising Iraqi and non-OPEC output could lift supply by around 1.9 million bpd above today's levels.''