The national average price of gasoline has fallen to a level not seen in more than five years, as it slid 15.1 cents to $2.403 for the week ending Dec. 22, according to federal data.

The average price of a gallon of regular unleaded last reached this level on May 18, 2009, when prices averaged $2.309. Gasoline costs 86.8 cents less than it did a year ago, according to data from the U.S. Energy Information Administration.

Gasoline fell in nine regions tracked by the federal agency. The sharpest decline came in the Rocky Mountain region, where it fell 20.2 cents to $2.384. The Gulf Coast region remains the cheapest at $2.176.

The average gasoline price costs at least $3.50 only in Hawaii ($3.585) and has fallen below $2.50 per gallon in 30 states. In Missouri, gasoline averages $2.074 per gallon. Texas is the third lowest at $2.164, according to the AAA's Daily Fuel Gauge Report.

Meanwhile, the average price of diesel fuel fell 13.8 cents to $3.281. Diesel costs 59.2 cents less than it did a year ago.