The national average price of gasoline fell 1.8 cents to $3.454 for the week ending Aug. 25, marking a continued decline that began in early July, according to federal data.

The national average price has fallen for seven consecutive weeks, bringing the cost of a gallon of regular unleaded to 9.8 cents lower than a year ago, reports the U.S. Department of Energy. Eight of the nine regions tracked by the federal government fell during the week. The sharpest decline came in the Central Atlantic with a 3.5-cent drop. The Midwest increased two-tenths of a cent.

The average price per gallon now costs at least $3.50 in 18 states and the District of Columbia, according to the AAA's Daily Fuel Gauge Report.

Meanwhile, the national average price of diesel tell 1.4 cents to $3.821 per gallon. Diesel fuel is now 9.2 cents lower than it was a year ago.