The average U.S. price of regular-grade gasoline dropped 2 cents over the past three weeks to $3.39 per gallon.

Industry analyst Trilby Lundberg of the Lundberg Survey said Sunday that prices at the pump could start increasing again because crude oil costs are rising.

Nationwide, the highest average price for regular-grade gas is in the San Francisco Bay Area, at $4.74 per gallon. The lowest average is in Houston, at $2.79 per gallon.

According to the survey, the average price of diesel is $3.64 a gallon, down a penny.