The national average price for a gallon of diesel fell 1.9 cents to $2.773 for the week ending May 13, according to the Energy Information Administration.

Prices fell in all regions except the Rocky Mountains where prices actually increased 0.3 cents to $2.998. That region also took the dubious honor of being the most expensive in which to fill up.

Meanwhile, prices took the biggest plunge in the Gulf Coast region, down 3.1 cents to $2.713. The Lower Atlantic was the cheapest region in which to fill up at $2.711 after a 2.4-cent drop.