Speeding And Your Vehicles Mileage

According to the U.S. Department of Energy (DOE), as a rule of thumb, you can assume that each 5 mph you drive over 60 is like paying an additional $0.21 per gallon for gas.  So, the Fuel Economy Benefit is between 7 and 23 percent. The equivalent gasoline savings is $0.21 to $0.71 per gallon.

Read more about it at the Consumer Energy Center website.