The average price of a gallon of regular-grade gasoline fell about a penny nationally over the past two weeks, to $2.31.
Industry analyst Trilby Lundberg of the Lundberg Survey said Sunday that the drop comes amid plentiful supplies of both crude oil and gasoline.
She says gas prices have declined more than 15 cents since April.
Gas in San Francisco was the highest in the contiguous United States at an average of $3.00 a gallon. The lowest was in Jackson, Mississippi, at $1.92 a gallon.
The U.S. average diesel price is $2.51, down 2 cents from two weeks ago.