The oil producers' cartel Opec has agreed to make a record cut in output, slashing 2.2 million barrels per day from its current supply.
Opec has made two other cuts since September, meaning it has cut a total of 4.2 million bpd in four months.
Despite the record cut, oil prices continued to fall as US data provided fresh evidence of falling demand.
US light, sweet crude for January fell as low as $39.94 a barrel, its first time been below $40 since July 2004.
Opec said that it hoped the record cut would boost prices but that it had no formal price target.
The cut means that the target for production for the 12 member states is now 24.845 million bpd.
Prices have been falling amid concern about how much less oil will be used by countries experiencing recessions.
Falling consumption means that industrialised nations currently have stockpiles of oil equivalent to 57 days of consumption - supplies that would typically be about 52 days at this time of year. Src:bbc news