Off brand gasoline



I drive a 1997 Subaru Legacy with 95,000 miles on it. Recently I had to have the catalytic converter replaced. The mechanic told me it was due to using “cheap gas”. I did, in fact, change to a supermarket brand gas about a year ago due to it being about 20 cents less a gallon than any other station. But I had always heard that off brand gas was really the same and the rumors that it was bad for your engine were b-o-o-o-ogus. Now I’m not so sure. Anyone with real information about this?


The real truth is that nobody (including the people who run the “offbrand” gas station) can tell you the exact origin of the gasoline sold there. There are actually very few refiners in this country (Valero may be the biggest at this point IIRC) who produce the gasoline that is then blended with proprietary additives and sold by the big name oil companies.

So, essentially, gas is gas. What does differ is the blend of additives that go into the gas after the refiner produces it. Some additives are more effective than others and the off-brand gas may not have any additives, or it may have a weird mix of additives from multiple brands of gas that have been mixed together. There is undoubtedly no consistency in that off-brand gas from one week to another, as a result of buying small lots of gas from many sources.

To get an idea of what a difference the additives can make, go to:

Personally, I can report that Shell gasoline (one of the top-tier brands) cleared up driveability problems that one of my friends was experiencing from steady use of Sunoco gas. I find that my car runs better on Shell than on other brands available in my area. As with other things in life, your experience may differ.


It won’t ruin anything but their are subtle differences between the fuel.

I used to work at a convience store/fuel station in college that was non-branded. What we had in the tanks was the ends of fuel trucks with branded fuel (eg Mobil, Shell etc) that did not want to return to Boston fuel depot with partial loads. So they sold it to us at a cut rate. So we had blend of all fuels in our tanks even sometimes premium mixed a bit into our regular tanks.


I know people who drive tanker trucks for a living. At any given refinery there are many tankers, some labeled and some not, filling up with the same product. They deliver to branded and non-branded gasoline stations alike. I buy my gasoline wherever it is convenient and/or inexpensive, and I don’t think, in general, that there’s enough difference to matter.

I do, however, believe that there might be something to the “Top Tier” brands (, and if one of those brands were available in my area I would probably use it.

I fill up at “Top Tier” brand stations (such as Shell) when I’m out of town.

I find it hard to believe that the gasoline you used is responsible for the catalytic converter replacement.

If your car needs Premium (which it might) and you use Regular, that’s another story.


Don’t blame the demise of the catalytic converter on off-brand gasoline. It is true that lead and other heavy metals in fuel can ruin the cat, but gasoline refiners take pains to remove all traces. (They don’t want to get in trouble with the EPA, which is very fussy over these matters.)

If cheap gas were truly harmful it would affect everyone’s car and word would spread fast. This hasn’t happened. You may continue to use the bargain gas without any qualms.


“Recently I had to have the catalytic converter replaced.”

Why?? Why exactly did the converter need replacing? Whatever the reason, the brand of gasoline you use had NOTHING to do with it.

Catalytic converters start to degrade immediately, from day one, just like the rest of the car. At some point they ALL fail and when this point is reached is caused by MANY factors, but NOT the brand of gasoline…


Catalytic converters shoulddlast longer than that. My old Chev Caprice had 325,000 miles on it when sold, and it still passed the emission test with the original converter. The main reason they go is when your car goes out of tune, such as spark plugs not firing propeerly or running too rich a mixture of gas to air. Another reason might be physical damage from hitting something. Your mechanic is guessing rather than diagnosing.

Having said that there are two types of off brand gas. The first is the supermarket gas which is the same as typical oil company gas because that is exactly what it is! Tell your mechanic that in France 55% of all gas is supermarket gas and French cars are running just fine! The other kind, and avoid this type, is the country ma & pa convenience store which also sells gas. They often buy off-season gas (the octane of gas is adjusted seasonally) and summer gas in the winter may make your car hard to start. The old tanks also could have water in them and other impurities. The supermarkets, on the other hand have newer tanks, and sell lots of gas so it is always fresh.

Go to another mechanic, one who can tell you exactly why your converter failed, if, indeed it did fali.