ATLANTA (CNN) - Gas prices shot up nearly 15 cents over the past two weeks to a national average of $2.50 per gallon of self-serve regular, according to a survey released Sunday.

"Higher crude-oil prices and higher costs from this year's new regulations affecting gasoline recipes are the two main drivers of the price surge," said Trilby Lundberg, publisher of the Lundberg Survey, which compared prices at about 7,000 gas stations on March 24 and March 10.

Prices have risen about 37 cents since Dec. 2, when they bottomed out at $2.13 per gallon.

Accompanying strong world demand for oil is concern about future oil supplies and instability in oil-exporting countries, particularly Iran, Iraq, Nigeria and Venezuela. Lundberg predicted more price increases later in the spring, "when our big driving season kicks in."

Prices were driven higher, in part, because refiners were working to complete maintenance and repairs ahead of the high-demand summer months, which requires idling some refinery capacity, she said.

Some of those projects are related to government-mandated requirements for ethanol blending and lower sulfur emissions, both of which kicked in Jan. 1.

Drivers in Salt Lake City paid the least, at $2.25 per gallon of self-serve regular. Drivers in Honolulu paid the most, at $2.80, Lundberg found.

Here are prices in other cities: St. Louis: $2.33; Las Vegas: $2.44; Atlanta: $2.44; Boston: $2.45; El Paso, Texas: $2.45; Seattle: $2.52; San Francisco: $2.65.

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