"As uncertainty surrounds both the European debt situation and the global economy generally, crude remains highly volatile and under the influence of general market sentiment. Hence, equities sell off, the dollar strengthens and crude heads lower," Matt Smith, analyst with Summit Energy, a subsidiary of Schneider Electric, told MarketWatch.com.
Other energy commodities were mixed at the end of Friday's trading session.
Gasoline gained less than a penny and closed at $2.62 a gallon.
Home heating oil lost 1 cent to $2.80 a gallon.
Henry Hub natural gas was off 7 cents, closing at $3.671 per million British thermal units.
At the pump, the national average price of unleaded gasoline dropped 1 cent from Thursday to $3.445, AAA said.