The national average cost of a gallon of on-highway diesel fuel rose slightly to $2.878, continuing a four-week streak of price increases, according to weekly figures from the Department of Energy. Despite the increases, the price is $1.07 cheaper than at this time a year ago.

Price increases were minimal in most parts of the country, with the largest average rise occurring on the West Coast excluding California, where a 3.1 cent increase brought the price to just over $3.00 per gallon. The lowest increase occurred in the Rocky Mountain region, where prices rose just under 1 cent to $2.772 per gallon.

The highest average price per gallon for diesel fuel is predictably still in California, at $3.25, while the lowest average price was the Gulf Coast at $2.771 per gallon.

The national average cost of a gallon of gasoline also increased this week, gaining 2.7 cents to $2.691. Gasoline is also much cheaper per gallon than a year ago by 97.7 cents.

Gasoline prices averaged anywhere from a high of $2.948 in California to a low of $2.436 in the Gulf Coast region.

The price of crude oil was just under $60 per barrel at $59.92 on the New York Mercantile Exchange. Prices were boosted by news of declining production from U.S. shale oil.