I work in the largest Refinery on the West Coast. We produce about 120,000 to 140,000 Barrles Per Day (times 42 for gallons = 5.04 to 5.88 million gals a day) of MOGAS. All gasoline *specs* are the same (for LOCATION) The Sierra's will get a different RVP spec, and everyone knows Ca gets a special blend. We ship via pipelines to everyone -- and they ship to us when we have shutdowns, shortages, etc. It's very common to see Exxon, Shell and many other trucks loading in our racks.
What basically sets the difference between brands, is the additive package. We can buy brand X, and mix our additives, and BLAM! It's now Chevron.
We only ship Premium, and regular. The mid grade is MIXED at the pump.
I am certainly no expert, but the above I know to be true...FWIW.
Mitch
PS If you ever saw a graphic indicating ALL of the pipelines running across this nation, you would be very surprised...