Chart courtesy of UMTRI.

Chart courtesy of UMTRI.

The average fuel economy of new light-duty vehicles sold in May climbed higher to 25.6 miles per gallon, according to University of Michigan researchers.

The EPA window-sticker rating for May new-vehicle sales increased 0.4 mpg from April, and likely reflects the continuing high price of gasoline, said Michael Sivak, director of the university's Transportation Research Institute.

New light-duty fuel economy is up 5.5 mpg since October of 2007, the first month the institute began its tracking.

The institute's Eco-Driving Index remained at 0.78 in March. The index estimates the average monthly emissions of greenhouse gases generated by an individual U.S. driver. The lower the number, the better. The current value represents a 22 percent improvement from October of 2007.