New York's main contract, light sweet crude for delivery in December, shed 42 cents to $86.67 a barrel and Brent North Sea crude for December delivery slid 30 cents to $107.87.
Concerns about crude demand in the US and Europe were pulling prices south, said Jason Hughes, head of premium client management at IG Markets Singapore.
"Reports that a couple of refineries in the US will remain closed and expectations that European manufacturing will remain muted signals weak demand," he told AFP.
Two US refineries with a combined crude processing capacity of 308,000 barrels a day, which closed when superstorm Sandy hit Monday, were still awaiting post-storm assessments before reopening, media reports said.
Their continued closure highlighted a slump in demand from the world's largest oil consumer after Sandy devastated the east coast, with millions left without power and damage estimated at up to $50 billion.
Traders were also skittish about the release of the closely-watched Markit eurozone purchasing managers index survey later Friday, with the market expecting it to fall to a two-month low.
