New York's benchmark contract, light sweet crude for delivery in September, climbed to a new historic peak of 44.77 dollars per barrel in pre-opening electronic dealing after reaching a record close Thursday of 44.41 dollars.

In London, Brent North Sea crude oil for September delivery shot up to a new all-time peak of 41.50 dollars per barrel in electronic deals.

By late morning in London prices were up four cents at 41.16 dollars.

"The uncertainty over Yukos seemed to have abated at the beginning of the week (but) has now returned," said Prudential Bache broker Tony Machacek.

Prices were also lifted by news of a fire late Thursday at a BP gasoline refinery in Houston, Texas, though BP said Friday the refinery unit itself was undamaged by the fire and had resumed operations.

"The fire certainly adds to the bullish elements in the market. However there is a limited reaction in actual gasoline prices," Machacek said.

Growing anxiety about the potential effects of high oil prices have set stock markets sharply back.

Analysts said the oil market's reaction to news that Russia had backtracked on a decision to allow the troubled oil giant Yukos access to its bank accounts underscored the lack of spare capacity in the world oil industry.

New York's West Texas Intermediate (WTI) light sweet crude could test 45 dollars a barrel within days and could even breach 50 dollars during the US and European winter, they warned.

"We're expecting prices to come off in the third quarter, but there remains a possibility that this winter, if we have a supply loss or if simply demand doesn't slow down, then at some times you could see WTI test 50 (dollars)," said Societe Generale economist Deborah White.

"We're in uncharted territory. No one knows. But if the market reacts this way to a relatively small supply loss then think what happens if we had major problems in Iraq or if Yukos were out for even weeks."

Yukos will be forced by the end of next week to shut down rail shipments that account for a quarter of its export trade if its bank accounts remain frozen.

"If Yukos can produce then there should be someone in Russia who can step in, buy the oil and pay to get it transported," said White.

"But there's likely to be some disarray as that occurs."

Russia's justice ministry said Thursday it had "recalled" an earlier decision allowing Yukos to access its current accounts to keep its operations running while paying a massive tax bill.

All of the financial resources that have or will enter the company's accounts would be seized or channeled into the Russian government's budget to pay off the tax debt, the ministry said.

Traders largely shrugged at OPEC's latest reassurances that it was on standby to increase oil supplies by up to 1.5 million barrels per day (bpd) to help to cool prices.

"We are ready to increase production between 1.0-1.5 million bpd and this issue will be discussed in the September 14 meeting in Vienna," OPEC president Purnomo Yusgiantoro told reporters in Jakarta.

The oil price surge punched the blue-chip Dow Jones industrials average below 10,000 points on Thursday for the first time since July 26. The Dow slumped 163.48 points, or 1.61 percent, to 9,963.03.

Worries about sky-high energy costs also drove the Tokyo Stock Exchange's benchmark Nikkei-225 index down to close below the 11,000-point mark for the first time in some 10 weeks.

In Europe the British FTSE 100 index lost 0.47 percent to 4,392.50 points, the German DAX 30 declined 1.44 percent to 3,773.94 points and the French CAC 40 slid 1.01 percent to 3,586.49.

In Tokyo the yen fell against the dollar, partly owing to oil-price considerations.