The price of crude oil closed above $80 a barrel for the first time on Thursday, as a hurricane in Texas raised supply concerns.
Texas production could be threatened by Hurricane Humberto
US light, sweet crude hit $80.20, two cents higher than the price it touched on Wednesday, though fell back to end the day up 18 cents at $80.02.
Meanwhile Brent crude for October fell 28 cents to $77.40.
Hurricane Humberto cut power to several refineries, adding to concerns about falling oil stocks.
Oil prices have risen 30% this year and are four times their 2002 level.
When inflation is taken into account, current prices are still some way below the all-time high of about $90-$100 a barrel reached in 1979.
That year, output from Iran - a key Opec member - collapsed following an Islamic revolution. The next year, war broke out between Iran and Iraq, another Opec member.
Still, analysts warn that the present situation is driven more by changes in the world economy, and less by shock events.
Hasan Qabazard, director of Opec's research division, said a spread of factors had caused the spike in oil prices.
"We have a storm working its way to American facilities. We have an economic crisis, so many things are affecting... prices." Mr Qabazard said.
Demand has soared in recent years, as China and India, in particular, have ramped up the fast-growing economies of their massive countries.
Production and refining capacity have struggled to keep pace, while heavy speculation in contracts for future oil deliveries has also helped keep prices high.
The most recent move by Opec - an increase of 500,000 barrels a day in the 12-nation group's quota - was little more than an "underwhelming gesture", said National Australia Bank analyst Gerard Burg.
Opec members are already pumping about a million barrels a day more than quota.