Gas jumps 25 cents in three weeks

(CNN) -- Gas prices jumped nearly a quarter in the past three weeks, but the trend is unlikely to continue, according to a survey published on Sunday.

The average price of a gallon of self-serve regular is $2.30, according to the May 15 Lundberg Survey of some 5,000 gas stations around the country. The 25-cent hike is the largest increase in gas prices on a weekly basis since a year ago, but "that's where the similarity ends," according to survey publisher Trilby Lundberg.

"It isn't very unusual for a price hike of this magnitude this time of year," she said. But, she added, "The prices cannot catch up with last year" when gas prices were averaging $3.80.

Drivers tend to take advantage of the longer daylight hours in June, July and August. In addition, gas prices are affected by the government's reformulation requirements, which include limits on vapor pressure and levels of ethanol, a corn-based additive that has increased in price as well.

Despite those factors, an increase in gas prices is "not necessarily going to continue, especially at this rate," she said.

The city with the lowest average price in the latest survey was Phoenix, Arizona, where a gallon of self-serve regular cost $1.99. The highest average was in Chicago, Illinois, at $2.63.

Here are the average prices in some other cities:

- Birmingham, Alabama $2.13

- Houston, Texas $2.16

- Denver, Colorado $2.19

- Atlanta, Georgia $2.19

- St. Louis, Missouri $2.20

- Boston, Massachusetts $2.28

- Long Island, New York $2.44

- Los Angeles, California $2.47

- Seattle, Washington $2.50