It can get even worse. Here in California we periodically read in the paper that the State or EPA caught someone selling gasoline that was not 100% gasoline.

You see, here in California, it is extremely expensive to get rid of used industrial solvents, especially chlorinated ones. We also have very high fuel taxes.

You do the math.

Truckloads of used industrial solvents have a way of mysteriously getting dumped in gasoline bulk tanks in the middle of the night. If it is straight petroleum solvents, like benzene and toluene and maybe a little cold cleaner degreaser solvent, it's no big deal and it burns more-or-less OK in most cars, since it is a very small fraction of the total tank. If it is chlorinated, it cleans things up real well but it doesn't burn too well and it rusts the heck out of everything down-stream of the pistons.

That's why I pay extra for the peace of mind that comes with buying name-brand gasoline. There can still be hanky-panky, but it is not so likely.