[Old182]

I'm sure others (MikeK?) can add to this, but simply put gasolines are composed of a couple hundred different molecules, primarily paraffins, aromatics, and olefins. Certain paraffins are great (isooctane) components because of their high octane and clean burning characteristics, and aromatics (toluene [methyl benzene] and xylenes [dimethyl benzenes]) are also high octane and help to provide range but tend to create soot during combustion. Olefins, however, typically come from cracking operations at the refinery and, because of their double bonds, are reactive. These are the "molecular nymphomaniacs" that react with oxygen leading to oxidation of the fuel. Once a free radical is formed, it can form a peroxide radical which then reacts with another and another and another until high molecular weight materials are formed - gums. Antioxidant products such as StaBil and others tie up these free radicals and prevent or stop the oxidation process (much the same as dark chocolate in our diets). That's the mechanism. The good news is that because olefins are known bad actors, their inclusion in gasolines has been on a downward trend over the last 10 years or so making fuels more stable than they used to be. I agree with HW regarding storage of a dry system; it can lead to far worse problems than skunky-smelling gasoline. I've never used antioxidants, but unlike a lot of snake oils out there, they are products that do work as their chemistry is sound. $0.02.