The average U.S. price of a gallon of gasoline has dropped a penny over the past three weeks.
The Lundberg Survey of fuel prices released Sunday says the price of a gallon of regular is $3.59. Midgrade costs an average of $3.77 a gallon, and premium is $3.91.
Diesel remained unchanged at $3.90 gallon.
Of the cities surveyed in the Lower 48 states, Chicago has the highest average at $4.10. Charleston, S.C., recorded the nation's lowest average price for gas at $3.27.
AAA Chicago Motor Club attributed the spike to refinery issues in the Midwest region and predicted the price to balance out at a constant rate in the month of June.
Despite the lower numbers in the city, however, Chicago prices remain the highest in the nation.