Retail gas prices across the country climbed an average of nearly 15 cents in the past two weeks, according to a survey released Sunday.

The weighted average price for all three grades increased to $2.52 a gallon by Friday, according to Trilby Lundberg, who publishes the semimonthly Lundberg Survey of 7,000 gas stations in the country.

Gas prices are 40 cents higher than they were a year ago.

Self-serve regular averaged $2.49 a gallon nationwide in the latest survey. Mid-grade cost $2.59 a gallon while the price for premium was $2.69.

Among stations surveyed, the lowest average price in the country for regular unleaded was in Salt Lake City, at $2.25 a gallon. The most costly was in Honolulu, where drivers paid $2.80 a gallon.