I don't think so. If gas was all the same I would buy it from the cheapest place. I made the mistake of buying gas from Citgo once, since then I don't believe all gases are equal.
WRONG... Shell V-Power gas has detergent that protects your car from gunk and all that crap and prolongs your car's life significantly... Kroger/non-brand gas screws up the engine and causes build ups that would end up costing you way more in repairs/new car.. Shell for the win, pay them at the pump right now better than at the shop later on..
My friend works for a company that adds additives into the gas that supposedly makes your car run better/cleaner. Those things can be found on some WalMarts and HEBs that have gas stations.
Costco and Sam's when in North Texas... But when back home in South Texas I find a Buc-ee's or a Conoco.