U.S. crude and Brent futures dropped to fresh 5-1/2-year lows on Monday as worries about a surplus of global supplies amid weak demand continued to drag on oil markets.

Brent crude LCOc1 reversed early gains to trade near $57 a barrel on Friday, as the glut of oil that has halved prices since June overshadowed investors repositioning at the start of the year for an eventual recovery.

Oil prices fell on Wednesday to a 5-1/2-year low and ended with their second-biggest annual decline ever, down by half since June under pressure from a global glut of crude.

Brent oil extended losses into a fourth session on Tuesday, with prices hovering close to a more than five-year low above $57 per barrel, as persistent worries about a global supply glut offset concerns about output disruptions in Libyan.

Oil prices fell Friday, tumbling as the dollar strengthened and as a supply glut in top consumer, the United States, trumped worries about falling production from Libya.

Brent crude futures held above $60 a barrel on Friday as strong U.S. economic data supported the market, but oil prices were track for their fifth straight weekly decline as a building supply glut capped gains.

The average price of a gallon of gasoline in the United States fell 25 cents in the past two weeks, tumbling to its lowest level in more than five-and-a-half years, according to the Lundberg survey released Sunday.

Brent crude oil slipped on Friday to below $63 a barrel, its lowest since July 2009, on persistent concerns over a global supply glut and a sluggish demand outlook.

The dollar rose on Friday after upbeat U.S. data suggested weaker oil prices are providing additional momentum for the American economy, which also underpinned Asian shares.

Brent rose to $71 a barrel on Wednesday, recovering some of its losses from the previous session as a turbulent market searched for a price floor after a nearly 40 percent fall since June.