Benchmark oil contract Brent North Sea crude slid to its lowest level since mid-2009 on Wednesday, having lost about half of its value since the middle of the year.
Brent North Sea crude for delivery in February hit $55.81 a barrel on the final trading day of the year, the lowest point since May 7, 2009. It later recovered slightly to stand at $56.08, down $1.82 compared with the close on Tuesday.
US benchmark West Texas Intermediate for February delivery was down $1.33 at $52.79, close to 5.5-year lows and also having shed around half its value in 2014.
The bulk of crude's losses have occurred since June, triggered by strong US stockpiles of oil and added to by OPEC's decision not to cut output to offset high global supplies.
Prices have been hit also by a stronger dollar, making commodities such as oil priced in the US unit more expensive for holders of rival currencies, and by slowing growth in China and emerging-market economies, a recession in Japan and a near-stall in the eurozone.
Daniel Ang, investment analyst at Phillip Futures in Singapore, said there are expectations for a rebound in prices in 2015.
He said the global supply glut could likely be alleviated by current low oil prices affecting "existing shale oil rigs, causing them to shut off, keeping US crude oil production in check".
The OPEC oil-producing cartel last month said it would maintain output levels despite ample global supplies caused in part by cheaper oil extracted from North American shale rock.
But stimulus measures by major economies could boost growth, and in turn, crude demand, Ang said in a commentary.
"In 2015 we believe that crude demand would be linked to how China, Japan and the eurozone perform. If we start to see the situation for these countries improve, a reversal from the demand side could happen."