(CNN) -- Gasoline prices climbed 10.73 cents over the past two weeks, to an average of $3.00 per gallon for self-serve regular, a national survey said Sunday.

The increase coincided with price hikes for crude oil, said Trilby Lundberg, publisher of the Lundberg Survey, which tallied prices at about 5,000 gas stations on June 23 and July 7.

Lundberg said uncertainties in world affairs were adding to the volatility in oil prices.

"The market has been extremely nervous," she said, citing tension over Iran's uranium-enrichment project and North Korea's rocket tests.

Though average gas prices had exceeded $3 per gallon in some cities, Sunday's survey results marked the first time since last September that the national price has hit the $3 mark, she said.

Gasoline prices could drop if geopolitical tensions affecting supply were to ease, but Lundberg said that was unlikely.

Growth in demand has leveled off because of recent price hikes, an indication prices may stabilize or drop modestly, she said.

"But we come back to the crude oil price and that depends on what the crude oil market does," Lundberg said.

Gasoline prices were 0.2 cents less than what they were last Sept. 9, shortly after Hurricane Katrina ravaged the Gulf Coast.

The cheapest gas was in Charleston, S.C., where drivers paid an average of $2.70 per gallon.

Honolulu drivers paid the most, at an average of $3.27 a gallon.

Other city averages:

Atlanta $2.96

Birmingham, Ala. $2.85

Denver $2.88

Chicago $3.25

Detroit $2.90

Dallas $2.90

Hartford, Ct. $3.14

Long Island, N.Y. $3.23

Los Angeles $3.23

Seattle $3.03

Washington $3.09

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