CAMARILLO, Calif. (AP) -- A national survey of gas prices reports that the average cost of U.S. regular grade gas dropped 18 cents per gallon in the last two weeks. Industry analyst Trilby Lundberg said Sunday that the average for regular grade gas is $3.08 per gallon, while midgrade averages $3.31 and premium $3.47. Retail diesel averages $3.67. Lundberg said the price has dropped 65 cents since its peak in May and is 29 cents below what it was last year. She said the drop has been driven by a decrease in the price of crude oil. She forecasts minimal further cuts if prices remain stable. In the Lower 48 states, San Francisco had the highest average price at $3.45 per gallon, while Memphis, Tennessee, had the lowest average at $2.73.