The average U.S. price of regular-grade gasoline jumped 5 cents a gallon (3.8 liters) over the past two weeks, to $2.97.
Industry analyst Trilby Lundberg of the Lundberg Survey says Sunday that gas prices have spiked 66 cents since early January.
But Lundberg says dropping crude oil costs could mean that prices at the pump will soon stabilize.
The highest average price in the nation is $4.14 a gallon in the San Francisco Bay Area.
The lowest average is $2.45 in Baton Rouge, Louisiana.
The average price of diesel rose 3 cents over the past two weeks, to $3.17.