Oil prices fell below $58 a barrel on Thursday amid ample US fuel stocks and the restart of two Nigerian oil installations following attacks last week. US crude settled down 83 cents to $57.88 a barrel, in volatile activity that saw trades as high as $58.96. London Brent crude eased $1.11 to $57.87 a barrel.
US crude prices are down 26 percent from their record hit in mid-July, as growing inventories and concerns over an economic slowdown spurred a sell-off.
Royal Dutch Shell resumed production of about 47,000 barrels per day at two of its in flow stations Nigeria.
Villagers stormed four facilities, including three operated by Shell, last week to press for contracts to supply speed boats and food to the facilities. One flow station remained shut, while Chevron reopened its facility earlier this week.
Separately, armed attackers in Nigeria on Thursday kidnapped a Briton and an American from an oil industry ship. Violence in the world's eighth largest oil exporter has cut oil output by about 500,000 bpd since February.
Adding pressure Thursday was data from the US Labour Department showing business productivity unexpectedly delivered no growth in the third quarter. Economic weakness could translate into slower energy demand, analysts said.
Traders shrugged off Wednesday's mixed US inventory report. US distillate stocks, including heating oil, fell by 2.7 million barrels and gasoline inventories dropped by 2.8 million barrels, the Energy Information Administration said.
"It seems that markets will respond to the EIA numbers in a big way only if there is truly a genuine surprise in EIA figures, and, on this account, this week's release fell a little short," said Man Financial.
Whether oil prices break out of the $56.55-$61.79 trading band they have maintained since early October may now depend on Opec's determination to carry out its first output curbs since 2004 and the intensity of the northern winter.
Saudi Arabia and the United Arab Emirates have told their customers to expect less crude this month, but most other producers have yet to commit.
Trade sources said on Thursday Algeria had cut November oil supply in line with its pledge with the Organisation of Petroleum Exporting Countries.
Exports from Opec should drop by 440,000 bpd through November 18, according to oil consultancy Oil Movements. Venezuela, one of the biggest price hawks in the cartel, said on Wednesday the curbs were meant to stop prices falling below $60 a barrel.