The average U.S. price of a gallon of gasoline has dropped 11 cents over the past two weeks.

The Lundberg Survey of fuel prices released Sunday says the price of a gallon of regular is $3.54. Midgrade costs an average of $3.72 a gallon, and premium is $3.86.

Diesel was down seven cents to $3.98 gallon.

Of the cities surveyed in the lower 48 states, Tulsa, Okla. has the nation’s lowest averageprice for gas at $3.21. Chicago has the highest at $3.97.