Josh Wardell’s MINI Cooper S

Earlier this month I mistakenly put regular 87-octane gas in my MINI for the first time ever. It gave me the opportunity to learn firsthand why Premium gas is actually the cheapest.

At the end of my mind-nummingly long commute, I stopped for gas just before home. The first pump was not responding, so I moved to the next one. Unfortunately I did not realize that the order of gas nozzles was swapped until I had finished filling the tank. For over 95,000 miles my MINI had never tasted anything less than 91, and now I fed the poor thing Somerville Vodka-grade gasoline.

Knowing the difference in grades technically is their ability to resist pre-detonation under higher compression, I babied my driving for the tank. Modern engines won’t allow themselves to get damaged, but they will be running at a less than ideal ratio to keep things safe when pushed. So I accelerated much more slowly than normal, forgoed flooring the pedal on the many opportunities I usually take during my commute, kept speeds down a notch. This activity will typically raise the gas milage of my commute from its average of about 28.5 mpg to about 30mpg (though in my opinion, that savings is not worth the loss of fun when it is most needed!)

I ran calculations at my next fillup. Despite the fuel-sipping driving, I only got 24.25mpg from the regular gas! That’s 17.5% worse than usual, or a whopping 23.7% worse mileage than what I would have achieved driving so tamely! Clearly the engine is compensating even at normal rpms, perhaps also there are more contaminants in the lower gas that do not burn as efficiently.

So what does that amount to? Sure, Regular is 25 cents cheaper per gallon. But The $2.59 I paid would be equivalent to $3.25 for the same number of miles I would have got paying $2.84 for premium! So clearly regular is much more expensive per mile. And these numbers would be even more extreme back when gas was above $4.

So the next time someone criticizes your car for taking Premium fuel, you can explain to them that it not only gives you a more powerful engine with better efficiency, it’s also much cheaper!