I hate to break it to all you brand loyal gas buyers, but it's all the same stuff (pretty much)! I mean literally, the same, except for the additives, some of which have questionable, if any, benefits.
I finance part of a major oil retailer/distributor (can't reveal their name), and I've been on a tour of their distribution facility and tank farm. Nearly all of the oil companies have inter-line distribution agreements, whereby they buy from each other's gasoline stocks and local tank farms, to save on distribution costs. So let's say for example the closest tank farm to your favorite Chevron station is owned by Citgo. Chances are that Chevron station is buying the base gasoline from the Citgo distribution center, as is the local Mobil, Exxon, BJ's, and the local no-name station. Now that doesn't mean the gas was made by Citgo, it's just stored by Citgo in their tanks. The closest refinery to the Citgo distribution center may be owned by Hess, who actually made the gasoline, from crude oil which could have come from anywhere. So technically, you went to Chevron to buy "Chevron gas", but you really got Hess made gasoline that was distributed by Citgo. You are getting Chevron additives, however, which are mixed in with the base gasoline at the time it is loaded on the truck at the Citgo distribution center. Those additives typically make up less than 0.5% of the gasoline by volume. And whether those additives actually do anything benefitial to your engine, is debatable.
But these inter-line arrangements are in place throughout the country with nearly every oil company and gasoline retailer. At the tank farms, all the gasoline is the same, stored in the same tanks, only separated by octane: 87, 89, 93, etc. That's it. There is no brand separation of gasoline. And all additives are done at the last minute when the tanker truck is filled before delivery to the station.
When I purchase gasoline, I'm more concerned with the cleanliness (lack of water or other contamination), and freshness of the gasoline, rather than the brand name or the additives. Because other than that, it's all the same!