The national average price of a gallon of regular unleaded gasoline continued its slide to around the $2.20 level with stations switching over to the winter blend, according to AAA.

Pump prices usually decline after Labor Day when many areas of the country switch from summer blend to winter blend, which is cheaper to produce and evaporates more easily. Winter blend must be able to evaporate at low temperatures for the engine to operate properly.

The average price fell 11 of the past 12 days ending on Sept. 12 and reached $2.18, according to AAA. The average price as tracked by the federal government saw a similar slide, falling 2.1 cents to $2.202. It is now 17.3 cents lower than it was a year ago, according to the U.S. Energy Information Administration.

The Midwest and Gulf Coast regions saw the sharpest declines, falling 4.5 cents to $2.135 and 3.2 cents to $1.973 respectively. Prices moved higher on the West Coast with a 3.8-cent increase to $2.632, the EIA reported. Meanwhile, the average price of diesel fell eight-tenths of a cent to $2.399. Diesel is now 11.8 cents lower than it was a year ago.

Gas prices in seven states are below $2.00 per gallon: South Carolina ($1.91), Alabama ($1.94), Mississippi ($1.97), New Jersey ($1.98), Texas ($1.98), Tennessee ($1.99) and Virginia (1.99). The biggest weekly decreases in price are seen in Indiana (-11 cents), Michigan (-10 cents), Ohio (-9 cents), Kentucky (-7 cents), Nebraska (-6 cents), Maryland (-5 cents), Minnesota (-4 cents), reports AAA.