The fuel economy for new cars sold in September averaged 25.3 mpg, a drop of 0.5 mpg from the value in August.
The Sept. average still represents an improvement of 5.2 mpg from October 2007, when researchers Michael Sivak and Brandon Schoettle of the University of Michigan Transportation Research Institute started compiling data.
"This large drop likely reflects the increased sales of light trucks and SUVs," according to a UMTRI statement.
Vehicles like the Chevrolet Silverado pickup, Toyota 4Runner midsize SUV, and the Nissan Rogue compact SUV helped drive those strong Sept. truck and SUV sales.
UMTRI calculates average sales-weighted fuel economy from the monthly sales of light-duty cars, pickups, SUVs, and vans and the combined city/highway fuel economy ratings that appear on vehicle stickers and in the EPA Fuel Economy Guide, according to Edmunds.
The latest UMTRI Eco-Driving Index shows that the average emissions of greenhouse gases generated by the driver of a new light vehicle purchased in September stood at a record-low 0.77.
The average price of a gallon of regular unleaded gas nationwide dropped to $3.28 on Monday, down from $3.44 a month ago, according to the AAA Daily Fuel Gauge Report.
AAA said we can also expect fuel costs to continue dropping in the "immediate future."
"Gas stations selling gas for less than $3.00 per gallon are growing increasingly common in some parts of the country," said an AAA statement. "Already, consumers can find at least one station selling gas for $3.00 or less in 26 states. Nearly 4 percent of U.S. stations are selling gas for $3.00 or less today, and this number should increase significantly over the next couple of months."
AAA said the reason for the drop in fuel prices include what AAA called a "dramatic boom in North American petroleum production" and the fact that no major hurricanes truck the U.S. coastline in September.
"Gas prices could fall another 20 cents per gallon by the time families load up the car for Thanksgiving. If everything goes smoothly, buying gas for less than $3.00 per gallon should be refreshingly common in many parts of the country this winter."