Years ago I argued that buying premium because you got better mileage was a fool’s deal. I based that on the math when gas was around $1.79 a gallon (remember that?) for regular and .20 more for premium. Then the math said that for it to be worth it you had to get 11.2% better mileage with premium (cost extra per gallon divided by the cost per gallon of regular). Which meant my 20 mpg car would have to get 22.24 mpg with premium – and the times I checked that I did not see that big of a jump.

Now, however, with gas at more than 3.50 a gallon – Let’s do the math:*

Regular $3.56

Premium $3.79

difference .23 or 6.5% more. So for it to be worth it a car that got 20 mpg with regular would only need to get 21.3 mpg for it to be worth the extra cost. A car that gets 27 mpg would need to get 28.8. I think I will try a tank or two – and see what I get.