The average price for a gallon of diesel nationally increased 3.4 cents to $2.98 for the week ending June 30, according to the Energy Information Administration (EIA).
All regions posted an increase except for California, which remained the most expensive region in which to fill up at $3.097, despite a 0.4-cent decrease. The biggest increase came in the Rocky Mountain region -- 6.5 cents to $3.052.
Despite a 3.6-cent increase, the Lower Atlantic region still had the cheapest diesel at $2.924.