The national average for a gallon of diesel dropped 1.1 cents to $1.70 according to the U.S. Energy Information Administration (EIA).
The decline marks the fifth straight week in a row of price relief and further reinforces EIA's summer outlook of easing fuel costs.
All regions posted a decline, except for the Lower Atlantic, which held at $1.636 per gallon. The Rocky Mountain region recorded the largest drop, down 4.4 cents to $1.835.
California remains the most expensive region to fill up - and the only region breaking the $2 mark, down 3.2 cents to $2.019. The cheapest region to fill up is the Gulf Coast, down 1.2 cents to $1.623.