The nation's average price of a gallon of unleaded fell 1 cent to $2.34 per gallon for the week ending May 15, which marked a third week of declining prices, according AAA.

Gasoline is 7 cents lower than a month ago and 12 cents higher than a year ago.

Prices have inched lower in the past few weeks as a result of an over-supply of gasoline. For this week, demand increased by 252,000 barrels. Most regions saw price declines, except for some states in the Great Lakes and Central regions. The coming weeks will bring the summer travel season, which could further increase demand.

The states with with the most expensive gas include Hawaii ($3.06), California ($2.98), Alaska ($2.90), Washington ($2.88), Oregon ($2.73) and Nevada ($2.68), Pennsylvania ($2.57), Idaho ($2.54), Washington, D.C. ($2.51) and New York ($2.50).

The states with the biggest changes in the last week include Indiana (up 9 cents), Ohio (up 7 cents), Michigan (up 7 cents), Delaware (down 5 cents), Kentucky (up 5 cents), Florida (down 5 cents), South Carolina (down 4 cents), Alabama (down 4 cents), North Carolina (down 4 cents) and Pennsylvania (down 4 cents).

Meanwhile, the average price of a gallon of diesel fell 2.1 cents to $2.544. Diesel is now 24.7 cents higher than a year ago, according to the U.S. Energy Information Administration.