Fuel economy of new vehicles sold in the United States has reached an all-time high according to a University of Michigan study.

The average fuel economy of cars, light trucks, minivans and SUVs purchased in October reached 24.1 miles per gallon, up from 23.8 mpgs in September. The mark is the highest since university researchers began measuring statistics five years ago.

Since researchers at the school's Transportation Research Institute began studying the fuel economy of new-car sales, fuel economy has increased by 20 percent, rising from 20.1 mpgs in October 2007 to 24.1 today.

Researchers estimate that the increase in efficiency has resulted in a savings of 6.1 billion gallons, enough to fuel all U.S. vehicles for approximately 13 days. It also amounts to a reduction of 120 billion pounds of carbon-dioxide emissions, according to the report.

The uptick in fuel economy underscores a shift in consumer preference for smaller cars as gas prices have risen and become more volatile over the same timespan. They also reflect the push for automakers to produce more fuel-efficient cars, as they seek to meet Corporate Average Fuel Economy standards.

"GM, Toyota and Honda increased their fuel economy the most over a year ago, as consumers continued to flock to small cars due to unseasonably high gas prices and compelling product" said Jesse Toprak, vice president of market intelligence at TrueCar.com.

Hyundai maintained the most fuel-efficient vehicle lineup overall at 27.5 MPGs, according to TrueCar.com., although that numbers may be skewed. On Friday, an EPA investigation revealed Hyundai and Kia's fuel-economy numbers had been overstated, in some cases by as many as 6 MPGs. Both automakers were forced to revise their fuel-economy numbers downward.

Behind Hyundai, Volkswagen maintained the most fuel-efficient vehicle lineup overall, averaging 26.6 miles per gallon across its fleet. VW increased 0.2 mpg from the previous year measured.

Of the eight manufacturers measured, Detroit's Big Three all ranked at the bottom of fleet-wide fuel economy. Chrysler fared the worst with an average fuel economy of 20.0 MPGs. GM ranked second to last with average fuel economy of 21.5 MPGs, although it had improved by 1.1 MPGs over the past year. Ford had a fleet-wide average of 21.9 MPGs.