The average U.S. price of regular-grade gasoline has dropped 12 cents a gallon (3.8 liters) over the past three weeks to $2.31.
Industry analyst Trilby Lundberg of the Lundberg Survey says Sunday that falling crude oil costs are the main reason for the decrease at the pump.
The average gas price has dropped 66 cents over the past 3 ½ months.
The highest average price in the nation is $3.46 a gallon in the San Francisco Bay Area.
The lowest average is $1.80 in Baton Rouge, Louisiana.
The average price of diesel fell 9 cents over the past three weeks, to $3.03.