The average price at the tank for a gallon of gasoline in the United States fell in the past two weeks, and should drop more as floods in the southeast curb demand and refiners and gas stations feel pressure to pass lower costs on to drivers, an industry analyst said on Sunday.

The national average price for self-serve, regular unleaded gas fell 9.24 cents on May 20 to $3.9074 per gallon, compared to $3.9998 on May 6, according to a nationwide survey of some 2,500 gas stations in larger metropolitan areas in the continental United States.

"We may well see a drop of another dime if crude oil prices allow," Trilby Lundberg, the survey's editor, told Reuters.

Refiners and retailers will be under pressure to pass on some of the savings from lower crude oil prices to motorists given the dampened demand for gasoline caused by the natural disasters and persistent U.S. underemployment, Lundberg added.

At $4.38 per gallon, Chicago had the highest average price for self-serve, regular unleaded gas, while the lowest price was $3.60 in Jackson, Mississippi.