The average U.S. price of a gallon of gasoline has increased 18 cents over the past two weeks.

The Lundberg Survey of fuel prices puts the average price for a gallon of regular at $3.69, about 8 cents higher than the same time last year.

Nationally, a gallon of mid-grade averages $3.84 and premium $3.96.

Analyst Trilby Lundberg attributes the increase to the high cost of crude as well as the partial loss of production at a refinery in Northern California.

Tucson, Ariz., has the nation’s lowest price at $3.18, while Chicago had the highest at $4