The national average price of a gallon of unleaded gasoline continued its summer decline, falling to $2.23 per gallon to reach the lowest level since early May, according to federal data.

The price fell 2.3 cents for the week ending July 18, and is now 57.2 cents lower than a year ago. Regional prices also fell as tracked by the U.S. Energy Information Administration. The average price in nine regions declined with the Lower Atlantic falling most sharply by 4.6 cents to $2.072 and the Central Atlantic falling 4.3 cents to $2.229.

Fuel prices continue to decline across the country due to "abundant fuel supplies and declining crude oil costs," according to AAA. Many areas are now seeing sub-$2 gasoline, which hasn't occurred in more than a decade.

Meanwhile, the average price of diesel fell 1.2 cents to $2.402 per gallon. Diesel is now 38 cents lower than a year ago.