The national average price for a gallon of diesel dropped 0.3 cents for the week ending June 18, according to the Energy Information Administration.

Not all regions posted a decline in prices, however, with the Gulf Coast reporting a 1.1-cent increase to $2.859. That region is still the cheapest in which to buy diesel, in spite of this. Both California and the West Coast regions posted the largest decline, down 3.2 cents to $3.185 and $3.117, respectively. California remained the most expensive region in which to fill up.

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