Gasoline is fungible, the only difference between brands is the additive. Unless you live near a local refinery, there is no way to tell where your gas was refined. It's traded between the oil companies all the time.
For example, if you buy Chevron gas but there is no Chevron refinery for 100's of miles then it's virtually guaranteed that the gas you bought was not refined at a Chevron refinery. They buy the gas from another refiner at the local truck rack and inject their additive (Techron) into it as it's being loaded onto the truck, then they deliver it to your local Chevron station.
If you stick with Top Tier providers you should be fine
http://www.toptiergas.com/retailers/