The national average price of a gallon of regular unleaded gasoline fell to $2.84 for the week ending Aug. 20, as driving demand wanes with the end of summer approaching, according to AAA.

This price level is three cents lower than it was in early August, and motorists in most states are seeing declining prices at the pump in a reversal from the increases seen in July.

"Compared to July, consumer demand for gasoline is weaning and prices are following suit," said Jeanette Casselano, AAA spokesperson. "The national average is expected to keep moving lower, especially with the switchover to lower grade gasoline in September."

The national price fell 2 cents from a week ago and 1 cent from a month ago. It has increased 50 cents from a year ago.

In September, gas stations begin selling a winter blend that's cheaper to produce and contains a fuel that evaporates at low temperatures so vehicle engines can operate properly, especially in colder temperatures.

States with the most expensive gasoline include Hawaii ($3.76), California ($3.60), Washington ($3.38), Alaska ($3.34), Oregon ($3.25), Idaho ($3.23), Nevada ($3.19), Utah ($3.18), Connecticut ($3.05), and Pennsylvania ($3.04).

States with the biggest changes for the week include Michigan (down 10 cents), Illinois (down 7 cents), Utah (up 6 cents), Florida (down 5 cents), Delaware (down 5 cents), Ohio (up 4 cents), South Dakota (down 4 cents), Georgia (down 3 cents), Oklahoma (down 3 cents) and South Carolina (down 3 cents).

Meanwhile, the average price of a gallon of diesel fell 1 cent to $3.207 per gallon, which is 61.1 cents higher than a year ago, according to the U.S. Energy Information Administration.