The national average price of gasoline remained essentially flat, rising 1.2 cents to $3.686 for the week ending June 16, according to federal data.

The price of regular unleaded is now 6 cents higher than it was a year ago, according to the U.S. Energy Information Administration. The price of gasoline rose in each of the nine sub-regions tracked by the agency, a division of the U.S. Department of Energy. The sharpest rise came in the Rocky Mountain region with an increase of 2.3 cents.

The average price of gasoline now costs at least $3.50 in 37 of the 50 states and the District of Columbia, according to the AAA's Daily Fuel Gauge Report.

Meanwhile, the average price of diesel fell 1 cent to $3.882 per gallon. Diesel is now 4.1 cents higher than it was a year ago.