Oil prices have jumped nearly fourfold since 2000 because of an array of factors: increased demand from China and India, declining production in Venezuela and Mexico, and supply disruptions from political crises in the Middle East and Africa and bad weather in the United States. Gasoline prices have periodically soared in recent years not only because of high crude prices, but also because of disruptions and tight capacity at American refineries.

A fast-moving but relatively weak hurricane, Humberto, formed in the gulf and plowed into Louisiana and Texas this morning, causing power outages and shutdowns at three refineries in Texas. The shutdowns are expected to last only a day or two, but traders said they remained concerned that other storms could disrupt oil production in the gulf. September is the peak month for hurricanes.

“It could have been a lot worse,” said Michael Rose, director of the energy trading desk at Angus Jackson in Fort Lauderdale, Fla. Mr. Rose said he thought that the $80.09 close on the New York Mercantile Exchange was close to “the crescendo top” and that within the next couple of months “I think we’ll go back to the 70s and then test the upper 60s.”

Recent price swings in crude oil came as hedge funds and other traders pulled back from investing in the oil market, distracted by a credit crisis roiling the financial markets over the last two months. But many traders got back into the market in recent days as they sensed that prices might move higher.

Not only are storms threatening production in the gulf, but the oil market was generally unimpressed by an announcement this week from the Organization of Petroleum Exporting Countries. OPEC said it would increase output by a modest 500,000 barrels a day to put some downward pressure on prices, a tactic that has not worked.