The average retail price of a gallon of gas rose about four cents across the nation during the past two weeks, according to a survey released Sunday.

Self-serve regular averaged about $2.95 a gallon, up from $2.91 two weeks ago, said Trilby Lundberg, who publishes the nationwide Lundberg Survey of roughly 7,000 gas stations.

The average price of mid-grade was $3.04 a gallon, up from $3. Premium hit $3.14 a gallon, compared with $3.10 two weeks ago.

The survey covered the period from April 21 through May 5.

Of the stations surveyed, the highest average price in the nation for regular unleaded was found in San Diego at $3.41 a gallon. The lowest was in Cheyenne, Wyo., where drivers paid an average of $2.61 a gallon.

Among the California cities surveyed, Stockton had the lowest average price for regular unleaded at $3.19.