In New Jersey, officials said prices would be checked in the state's 21 counties.
"We would hope that no one in New Jersey would attempt to exploit this tragedy for monetary gain," Acting Gov. Donald T. DiFrancesco said.
The two states can prosecute offenders under consumer-protection laws.
At a news conference yesterday, Pennsylvania Lt. Gov. Mark Schweiker confirmed reports of retail price increases of as much as 15 cents a gallon.
"We have been assured by the industry . . . that the gas supply is ample and sufficient," he said. "There is no need to think about panic purchases."
One Pennsylvania gas station owner who was found selling at prices 20 cents above wholesale was facing prosecution, officials said.
So far, that does not seem to be the case in the Philadelphia area, where the increases appear small compared with those at gas stations in Oklahoma and other states, where prices were jacked up to as much as $5 a gallon.
In Philadelphia, a random survey of gas prices at 16 stations revealed no evidence of price gouging. Prices ranged from $1.32 to $1.49 for regular unleaded gas.
The price of regular unleaded was $1.33 at an Amoco station at Cottman Avenue and Roosevelt Boulevard, the same as before the attacks.
The situation was different in the Philadelphia suburbs, where prices at some stations jumped 6 cents overnight.
Prices at a Wawa convenience store on Gay Street in West Chester went up 6 cents a gallon for regular gas Tuesday night, to $1.44, manager Chris Degama said.
He said corporate officials offered no explanation for the hike.
Michael McCleery, who was filling his pickup truck at an Amoco station on Paoli Pike in East Goshen Township, said he expected an increase.
"It reminds me of the Gulf war, when it took six hours for prices to [go up]," said McCleery, who lives in Harleysville, Montgomery County. "It all comes down to greed. It's a simple as that, because there is no shortage."
Philadelphia-based Sunoco Inc. said there was no reason to foresee any significant price increases.
"Our current appraisal of the markets is that we are adequately supplied," spokesman Jerry Davis said.
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Inquirer staff writer Bob Moran, suburban staff writer Susan Weidener and the Associated Press contributed to this article.