Save more gas switching from 15 to 18mpg than from 50 to 100mpg

I saw this on Eric de Place’s blog and although not immediately intuitive, he’s right:

You save more fuel switching from a 15 to 18 mpg car than switching from a 50 to 100 mpg car.

Driving 20,000 miles

15 mpg 18 mpg 50 mpg 100 mpg
1333 gallons  1111 gallons  400 gallons  200 gallons 

So going from 15mpg to 18mpg, you’d save 220 gallons, but doubling your mileage from 50mpg to 100mpg would only save you 200 gallons a year, assuming you drove 20,000/year. So it really is important to pay attention to the car you pick’s gas mileage, even if it’s only a few miles more per gallon than another one.