Today I was listening to Car Talk on NPR while driving, coincidentally, a car. Those guys are always good for some laughs, and sometimes I even learn something new about automobiles. Today was one of those days.

Tom and Ray Magliozzi (aka the Tappet Brothers) were in adamant agreement that most people should use regular gasoline, rather than premium, no matter what car they drive. They stated that the difference in performance is negligible (unless you’re racing), regular gas costs less, and premium gas may contain higher levels of MTBE (which can contaminate drinking water).

Hearing that made me go, “Huh?” I had always been told that using a higher octane gasoline would help prevent knocking and keep your engine running cleaner. So I decided to do some research.

Does your car need premium gas?

The FTC says to go with what the owner’s manual says, but that the usual octane recommendation is met by regular gas. However, Edmunds.com explains that for about the last fifteen years, on-board computers have been able to regulate knocking even at lower octane levels than are recommended by the manufacturer. And regular gas appears to run just as cleanly as premium. Both state that if your engine begins to knock, you should increase your octane level — but otherwise, go for regular.

What’s the fuss over MTBE?

MTBE is added to gasoline to raise its octane level and to oxygenate it. Oxygenation helps to reduce carbon dioxide emissions of pollutants, so the EPA encouraged the use of MTBE — until they found out that it’s also a carcinogen that mixes easily with ground water, and it often leaks from storage tanks.

Not all gasoline contains MTBE — some US states have already banned its use, and manufacturers are beginning to phase it out in preference for the more expensive (but not carcinogenic) ethanol. But if you live in an area that does allow MTBE, premium gas is likely to contain more of it, in order to raise the octane level.

The money

In the US now, the price of premium gasoline can be as much as 30 cents a gallon more than regular. That means that you could save three or four bucks on your average fill-up by switching to regular gas. If you fill up once a week, you could save $150 – $200 a year.

Fitting topic for [GAS], don’t you think? Given the information above, I’m ready to switch to regular — at least until someone comes a-knocking under the hood. How about you?