The national average price of gasoline fell 5.5 cents to $3.353 per gallon for the week ending Sept. 22, extending the fuel's price decline to three months. Gasoline last slipped below $3.30 per gallon in early February, according to federal data.

The summer price decline has brought the national average gasoline price to a level that's 14.2 cents lower than its price a year ago. The average price again fell in all nine regions tracked by the U.S. Energy Information Administration. The sharpest decline came in the Midwest where it fell 8.2 cents during the week to $3.275.

The price now costs at least $3.50 in 14 states and the District of Columbia, according to the AAA's Daily Fuel Gauge Report.

Meanwhile, the national average price of diesel fell 2.3 cents to $3.778 per gallon. Diesel now costs 17.1 cents lower than it did a year ago.