U.S. gasoline prices in the last month have fallen far more than the corresponding drop in the price of crude oil as the summer driving season ends with a huge oversupply of transportation fuel.

Gas prices plunged 9.7 percent in September, the largest monthly decline since October 2012, while crude oil prices fell by 6.7 percent in the same month, according to barchart.com.

“Most drivers are paying the lowest gas prices in more than eight months due to abundant gasoline supplies, the end of the summer driving season, lower oil costs and the switchover to winter-blend gasoline,” Avery Ash, a AAA spokesman, said on Tuesday. “Supply and demand is working in most consumers’ favor with consumption down and gasoline stocks more than 10 percent higher than a year ago.”

The average gas price in September was $3.52 per gallon, which was the lowest national average for this month since 2010 and 31 cents per gallon cheaper than the monthly average a year ago, according to AAA, which attributes the decrease in prices to refineries running with “relatively few problems,” especially as no hurricanes affected production in the past few months.