Traders said prices remained buoyed by data showing an unexpectedly large fall in US stocks. The American Petroleum Institute (API) and the Energy Information Administration (EIA) published data showing crude, distillates and gasoline stocks fell last week in the United States.

The data is closely watched as a barometer of the success of Opec crude supply cuts. The US consumes one-fifth of the world's oil.

The data propelled US crude futures to a 63-cent rally on Wednesday and Brent crude futures to a 41-cent rise. Opec aims to keep 4.3 million barrels per day of crude off the market in a programme that is due to run to the end of March.

Its target is to get global oil stocks down to levels last seen in 1996 and 1997. This week's US data showed that crude stocks stood at 294.4 million barrels on December 10, the lowest level since January 1997.

But although stocks appear to be matching Opec targets, cartel heavyweight Iran this week clearly signalled no let up in the cuts. Iran's Opec governor, Hossein Kazempour Ardebili said the cartel would maintain its cuts until their expiry. "Opec will under no circumstance raise its oil production ceiling until March," he said.

The cuts were reinforced earlier on Thursday with news that the National Iranian Oil Co, had told its Asian customers that supplies in January would be cut 12 per cent below levels covered by its long-term contracts.