Oil prices fell to a six-year low in New York on Monday (16 March), dipping below $44 (£30, €41) a barrel as the market priced in the prospect of an extended supply glut.
West Texas Intermediate crude fell as low as $43.27 a barrel at one point on Monday, its lowest level since March 2009.
Brent crude fell to $52.88 a barrel on Monday afternoon in London.
Crude oil futures contracts (agreements to buy or sell crude on a given future date) had fallen on Friday after the International Energy Agency (IEA) said US crude reserves were approaching storage capacity with no sign of a slowdown.
"Selling pressure was generated on Friday by the IEA, which warned that storage capacities could soon be exhausted in the United States," said analysts at Commerzbank, Germany's second biggest lender.
"The reason cited by the IEA was the massive oversupply, which stems first from and foremost from the still rising US oil production."
Meanwhile, the strengthening dollar currency has made oil purchases relatively more expensive around the world and has been a factor in weakening demand.
Crude oil prices have fallen by more than half since June 2014, amid weak demand from industrialised economies and a well-supplied marketplace, fuelled mostly by a boom in US shale oil production.
With the Organisation of Petroleum Exporting Countries (Opec) maintaining production levels in an attempt to protect its market share, prices continued to slide through to January 2015.
Analysts had begun to predict that oil prices had actually reached the bottom of the cycle in February, as prices rose around 20% in the month.
Monday's decline has proved those analysts wrong.