Brent crude oil slipped below $108 a barrel on Wednesday, extending five weeks of falls on signs of improving global supply.
Oil prices have tumbled over the past month as output has risen, with Libya ramping up production, while tensions over Syria and Iran have eased, dampening worries of disruption to production from the giant Middle East oilfields.
Libyan Oil Minister Abdelbari Arusi said on Wednesday oil output had risen to around half the level seen earlier this year, and full production could be restored within days once strikes that have blocked oilfields and ports are resolved.
"Supply is no longer a worry," said Carsten Fritsch, senior oil and commodities analyst at Commerzbank in Frankfurt.
"There is plenty of oil in the market and the risks are to the downside. We expected prices to fall further."
Brent crude for November fell 10 cents to $107.84 a barrel by 1100 GMT. The benchmark has fallen by more than 8 percent from a six-month high hit in late August.
U.S. crude traded around $101.80, down 24 cents, extending losses for a fourth straight session.
Data from the American Petroleum Institute (API) industry group show U.S. crude inventories rose by 4.6 million barrels last week and figures on Wednesday from the Energy Information Administration (EIA) are expected to confirm the trend.
The EIA is expected to report that U.S. crude oil stocks rose 2.3 million barrels in the week to Sept. 27, according to a Reuters survey of analysts.
The weekly API report, published late on Tuesday, said crude oil stocks at the U.S. Midwest delivery hub of Cushing, Oklahoma, the delivery point for the U.S. oil futures contract, fell by 83,000 barrels last week.
Cushing crude stocks have fallen for 12 consecutive weeks, EIA data show, but the pace of the drawdown has slowed as supply has improved and analysts say that a U.S. stock rebuild may now be under way. The EIA data will be released at 1430 GMT.
Investors have also expressed concern that a U.S. government shutdown may reduce demand for commodities such as oil.
Wrangling in the United States between President Barack Obama and congressional Republicans has forced the first government shutdown in 17 years. The shutdown has left hundreds of thousands of federal employees on unpaid leave and is expected to crimp demand in the world's largest oil consumer.
"That's going to hurt demand," said Jonathan Barratt, chief executive of commodity research firm Barratt's Bulletin, adding that geopolitical risks had also faded from view. "All the premium risk that was built into the oil market has evaporated. The bullish sentiment is just not there any longer."
The Organization of the Petroleum Exporting Countries expects demand for its crude to fall to 29.61 million barrels per day (bpd) in 2014, down 320,000 bpd from 2013, because of rising supply outside the producer group.
OPEC's Secretary General Abdullah al-Badri indicated in an interview with Reuters that the cartel may not make big changes to output policy at a December meeting, adding that he was "comfortable" with the market outlook for 2014.
"It is not a huge drop in the call on OPEC," Badri said.
OPEC, which pumps more than a third of the world's oil, meets on Dec. 4 to decide whether to adjust its output target of 30 million bpd. (Additional reporting by Jacob Gronholt-Pedersen in Singapore; editing by Keiron Henderson)