Motorists hitting the road in the last week probably haven't noticed much, but the national average is seemingly on its way lower. Average gasoline prices across the nation fell almost 2 cents per gallon in the last week to $3.63/gallon, or about a nickel more than a year ago.

Many states have seen some relief, and more is on the way for many, but I'll pinpoint Washington and Oregon as two states that may not see relief as quickly, and could temporarily see higher prices as tight supply put upward pressure on retail gasoline prices.

Some of the cheapest gasoline prices today in the U.S. are found in Oklahoma, where prices average $3.35/gallon, a 4 cent drop versus last week. Other states with among the lowest prices: Montana $3.37/gal, New Mexico: $3.39/gal, Arkansas $3.39/gal, Missouri $3.40/gal.

On the opposite side, Hawaii takes the cake with average prices of $4.36/gal. California stands at an average $4.17/gal, but that's 6 cents a gallon lower than a week ago and a dime lower than when prices peaked on April 29. Alaska, Connecticut, and New York round out the top five.

As you may have heard, the switchover to summer gasoline is complete and rolling out to pumps nationwide if it hasn't already. The blend costs more to produce, but will likely no longer be the reason for rising prices. Refinery maintenance is also winding down with most refineries having completed their work. This should help drive prices down in coming weeks as refineries boost production of summer gasoline and inventories rise.

Gas prices by Memorial Day will likely average $3.55/gal, with the cheapest states showing averages in the $3.20s. Nearly every state will see lower prices on the holiday than today, so plan accordingly.