The national average price for a gallon of diesel dropped 11.8 cents, to $2.595, for the week ending Sept. 24, according to the Energy Information Administration. That was 20.3 cents cheaper than prices during the same week last year.

The Rocky Mountain region had the largest rollback, posting a whopping 22.5-cent decline, to $2.827. That drop means the region had to relinquish the dubious honor of being the most expensive place to fill the tank. California, where prices were the most stable, now takes that spot, after a 9.2-cent decrease put its price at $2.91. The cheapest region in which to fill up was the Midwest, at $2.506, after shedding 11.8 cents.

For more information, go to http://tonto.eia.doe.gov/oog/info/wohdp/diesel.asp