his from a google search...
I worked for a fuel terminal company. This is how it works: Fuel is delivered in a very small number of pipelines. Terminals are the giant circular tanks that get their product directly from pipelines. If you're on the east coast, it's one of two pipelines. West coast, similar situation, different lines. The lines ship Premium, Regular, Diesel, and Jet fuel. Midgrade is a mixture Regular and Premium made at the time a tanker truck fills up at a terminal.
There are a handful of tanker truck operators in a given geographic area. Some consumer fuel providers, like Exxon, may have their own fleet of trucks. In any case, here's the important part. Every time a tanker truck driver (or the dispatcher) is tasked with obtaining fuel from a terminal, they select from the lowest price available among the local terminals. It's all the same fuel. They fill up the truck, and then deliver this fuel to the gas stations they service. The gas station owner does not care where the fuel came from.
Like in other businesses, there may be competitive agreements in place where, for instance, one tanker company gets a deal if they do business with one particular terminal. That has no effect at all on the fuel - remember - it's all the same fuel. If one terminal is out of Regular at the moment, the tanker drives to the next one and get Regular there.
What about additives? One particularly popular "special gas" sold by a particular company just contains two times the amount of the normal additive. This is keyed in by the tanker truck driver before he fills up the tanker at a terminal. Though the marketing for this particular product leads you to believe it's their own additive, it's not. It's the same as everybody else's, just twice as much.