Oil prices fell nearly 5% on Tuesday driven down by a gloomy economic outlook and news that OPEC made only two-thirds of its pledged supply cuts in November.
US crude settled at $US46.96 a barrel, down $US2.32, or 4.71%, the lowest settlement since May 2005.
London Brent settled at $US45.44 a barrel, down $US2.53.
Crude prices have now fallen from a record $US147.27 a barrel struck in July as the mushrooming global economic crisis hits demand in the United States and other large consuming nations.
In September, US oil demand fell to its lowest level for any month in more than a decade, the US Energy Information Administration said last week.
Members of the Organisation of Petroleum Exporting Countries had pledged to lower output by 1.5 million barrels a day for November in order to prop up prices, but were only 66% compliant with the target last month, a Reuters survey showed on Tuesday.
OPEC concerned about oversupply
OPEC members remained concerned about oversupply in the world oil market and may decide to cut output further at their next meeting in Algeria on 17 December.
"We are concerned about the glut ... I think there is an indication that we will have another cut," Qatar Oil Minister Abdullah al-Attiya said.
Top oil exporter Saudi Arabia has highlighted $US75 a barrel as a "fair price" for oil.
Meanwhile, sources said two OPEC members, the United Arab Emirates and Kuwait, will increase oil sales to many major Asian customers, sending mixed signals about OPEC output cuts.
More bearish news for oil prices could be in store on Wednesday, when the US government reports weekly oil inventory data.
A Reuters poll of analysts showed U.S. crude inventories likely rose by 1.7 million barrels last week, a third consecutive weekly build, as imports continued to increase.