Another point that everyone seems to miss is the the holy measurement--miles per gallon--is a lousy one. Look at some numbers--if you drive, say, 15000 miles each year and your old clunker got 10 mpg, you'd burn 1500 gallons of fuel yearly. Switching to one that got 15 mpg, you'd burn 1000 gallons per year. From a 50% improvement in mpg.

Now consider that if you had a car that got 30 mpg, and switched to one that got 60 mpg--a 200% improvement, and drove the same 15000 miles per year, your yearly consumption would go from 500 gallons per year to 250 gallons per year--a saving of 250 gallons. From a 200% improvement in mpg. In fact, if you started with a 30 mpg car and switched to one that got a million miles to the gallon, your savings would be less than what you got from switching from 10 to 15 mpg.

Gallons per mile--or per 1000 miles--is a much more meaningful statistic.