I also know that gasoline is considered a fungible product - the additive package is introduced when the truck loads at the terminal. That doesn't mean that Shell has the same additive package as Uncle Joes Convenience Store. It also doesn't mean that one tanker truck of Brand X is identical to the next tanker truck of Brand X.
I'll second this, based on the input of a friend who has run refinery operations for a few decades. All brands pull their tanker trucks to the same spigot for loading, at which point the additive package is added to the same refined gasoline. Case in point: Hawaii has two oil refineries, but all the same brands you'll find everywhere else. It's the same gas.