WASHINGTON - Soaring gasoline costs prompted thousands of complaints Thursday to federal officials about alleged price gouging and demands by some members of Congress for an investigation into gasoline markets.

The Energy Department reported more than 5,000 calls to its price gouging hot line from motorists around the country, although officials emphasized there was no way to immediately determine how many of the allegations were valid.

The states with the most complaints were North Carolina, Georgia, New York, Pennsylvania, Texas, Illinois, Tennessee, New Jersey, Michigan and South Carolina.

Meanwhile, attorneys general from a number of states held a telephone strategy session to discuss the rapidly escalating gas prices and possible investigations into gouging. Prosecution for price gouging is generally a state matter unless it involves some form of collusion or other activity in violation of federal antitrust laws.

Gas prices jumped 35 cents to 50 cents a gallon overnight in some areas, pushing to well over $3 a gallon, after Hurricane Katrina shut down nine Gulf Coast refineries, disrupted gasoline pipelines to the Midwest and East, and stopped 90 percent of the oil production in the Gulf of Mexico.

"If we get consumer complaints about (gasoline) prices, we'll look at those complaints to find evidence of anticompetitive conduct," said John Seesel, the FTC's associate counsel for energy issues.

But Seesel said the FTC has no jurisdiction over an individual gas station operator raising his price, no matter how high, unless there is some collusion among retailers. A number of states, however, have anti-gouging statutes. Following FTC policy, he declined to say whether any investigations were under way.

On Thursday, Attorney General Troy King of Alabama initiated a private telephone conference with a number of his colleagues from other states to discuss strategy in response to the rising gas prices and reports of huge overnight spikes by some gasoline retailers.

There have been isolated cases of unusually huge price jumps, including a gas station in Georgia that briefly charged $6 a gallon when competitors ran out of gas. In Michigan, there was a price jump of nearly $1 a gallon overnight, although prices then receded, according to Rep. Fred Upton, R-Mich., who drove around his district on Thursday to gauge prices.

"Prices are averaging $3.19. It's as high as $3.58, from $2.61 on Tuesday," said Upton in a telephone interview. "My sense is the supply and demand equation does not fit a 60-cent (a gallon) increase in the last 36 hours."