The national average price of gasoline fell 6 cents to $2.68 on the week in a continued "unusual" trend of falling prices after Memorial Day, according to AAA.

Following Memorial Day, prices usually inch higher toward the summer driving season, said Jeanette Casselano, AAA spokesperson. Prices are now 17 cents cheaper than a month ago and 20 cents lower than a year ago.

Domestic gasoline inventory increased 1 million barrels last week, according to the U.S. Energy Information Administration. The greater supply is pushing prices lower. Last week, gasoline demand reached 9.87 million barrels per day, which was the sixth highest weekly count on record, according to the latest EIA report.

"Growing gasoline inventories are contributing to relief at the pump as we head into summer," Casselano said. "Current U.S. inventories sit at nearly 235 million barrels, which is helping to feed growing demand."

States with the largest monthly decreases include Ohio (29 cents), Michigan (28 cents), Indiana (26 cents), California (23 cents), Mississippi (21 cents), Kentucky (21 cents), Illinois (21 cents), Tennessee (19 cents), North Carolina (19 cents), and Oklahoma (19 cents).

States with the most expensive markets include California ($3.81), Hawaii ($3.64), Washington ($3.41), Nevada ($3.41), Alaska ($3.38), Oregon ($3.28), Idaho ($3.10), Utah ($3.09), Arizona ($2.97), and New York ($2.86).

Meanwhile, the average price of a gallon of diesel fell 3.5 cents to $3.07, which is 17.4 cents lower than a year ago, according to the EIA.