Premium gas gives you more miles per gallon than regular gas.

Sorry, that's pretty much booo-gus.

Here's why.

Each gallon of gas that we pump from our local Quickie Mart is actually made up from as many as seven different ingredients. The exact amount of energy in each gallon of premium or regular gas will vary from company to company, depending upon what kind of additives they use.

In actual fact, you'll get a greater range of fuel economy between different brands of regular gas, than you will between the same manufacturer's regular and premium gasses. Interesting, eh? We thought so.

Finally, here's a nice irony: to increase gas' octane rating, companies add ethanol, when they're mixing up a batch of premium fuel. Interestingly, ethanol actually contains less energy than untreated gas, so the net result from the ethanol component is a reduction in your MPG. Other premium additives, however, have the reverse effect, and slightly increase your MPG. So okay, overall premium provides a very slight net increase in MPG, but it's so slight that we swear you won't notice the difference.

I always used the increased MPG that resulted from using premium as a justification to purchase it.

Too bad. Consider yourself better informed now, and stop lining the pockets of oil companies, okay?

Premium has special or extra detergents in it that are worth the added cost.

It's true that premium gas does contain special or extra detergents, but in our opinion they're of no additional benefit.

Our advice is to ignore any sales pitch about the super-special detergents that come in the premium-grade fuel.

These days, all of the gasoline from the major gas companies contain more than enough detergents to keep your engine clean. Period.

The only reason you might have a use for the extra detergents in premium, is if you have a noticeably dirty engine, and need to scrub carbon and other crud off engine components. (And, if you're doing that, we'd instead suggest that you toss in one of the many fine engine additives.)

You said "major gas companies." Is there a difference in the gas between the big names, and the El-Cheapo gasoline at my local Costco or Stupey-Mart?

There is. A number of years ago, some of the major auto manufacturers were ticked off with the deposits from gas that met EPA detergent standards. In other words, they were afraid they'd take the heat for problems, when their customer's engines clogged up from the twigs and dirt that was getting deposited on their fine handiwork.

So, they set their own guidelines, which they call "Tier 2." All of the gas from the major gas companies meets the Tier 2 standards. The gas at your local Quickie Mart probably does not. The difference? In some tests, after about 10,000 miles, there was a minor amount of crud built up on engine components that ran exclusively on Quickie-Mart gas. Do we think this is an issue? Not really. But, would we advise running your car for 100,000 miles only on Quickie-Mart gas? Not if you're concerned about the longevity of your vehicle. We recommend switching back and forth between Tier 1 and Tier 2 — maybe every other tank full — to keep your engine running clean.

I will void my warranty if my owner's manual calls for premium and I use regular unleaded.

You might, but we don't think so.

But, that's just our humble opinion. If you use regular instead of premium, and your car calls for premium, there's no way we can guarantee that your dealer won't try to sneak away from taking responsibility for repairs.

But, if we had a vehicle that called for premium, we'd take the risk. There's a big price difference between regular and premium. That adds up to quite a bit of money over the life of your car.

As a last ditch effort, print out this feature and show it to the dealer. Maybe he'll come to his senses. But don't hold your breath.

Using regular gas in a car designed for premium will definitely damage the engine.

We don't believe that any modern engine that claims to require premium will be damaged by using regular unleaded judiciously. Neither do any of the sources we've checked with — including the American Petroleum Institute, the American Engine Rebuilders Association — even a chemist (who would rather go unnamed) at a major gasoline company.