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.