Oil companies profit heavily on the uninformed consumer (which is about 95% of all the day-to-day gas buyers in the world)
Gasoline is gasoline...
The regular (87) octane all comes out of the same pipe no matter which station you purchase it from.
Cheaper gas generally has 10% ethanol in it except for states that mandate the ethanol content (I think Arizone, and maybe the summer blends in California maybe) which have to be stated clearly on the pump that the gasoline contains ethanol (Federal law).
Ethanol is cheaper, burns cleaner, is more environmentally friendly, but has an octane lowering effect so it dilutes the overall "power" of gasoline (thus it's general unpopularity -- you don't go as far as you could on 100% gasoline)
All gas stations obtain their gas from suppliers which are just basically terminals. These terminals suck gas out of the exact same pipeline. There are only 3 or 4 major gasoline pipeline routes in the US. (NE corridor being the longest route from the Texas Gulfcoast up to the New England states)
It is true that these terminals will add certain additives of the brands own individual formulation, but in the case of regular gasoline, you could run what was coming straight out of the pipe and never notice a difference.
Premium gas is handled differently. If you want to be a brand loyalist, you can be, but only if you buy higher quality gas than "regular"
Cheap gas also tends to get a bad rap in that it only takes one bad retailer to not seal his tanks properly and get water in the tank to make a certain brand have a bad reputation.
"How can they sell gas for $0.10 cheaper than the station across the street is? There must be something worng with the gas."
They're not selling it cheaper... The other company is selling it for more profit and has convinced you that it's worth it.
