http://www.edmunds.com/advice/fuelec...2/article.html
http://fueleconomy.gov/feg/driveHabits.shtml

I've got a used car with a mpg calculator. The car is rated for somewhere around 18mpg city. With light pressure on the pedal at 35mph, the sensor can get up to 60-70mpg. The key to driving efficiently is to drive as if you've got a champagne glass on the dashboard you're trying not to spill. That, and keep your car in its optimal mpg range for as long as possible. In almost all cars, it's somewhere between 30 and 50mph.