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The History Channel's Modern Marvels series did an episode on gasoline. Was on YouTube but it got removed. Might be able to find it elsewhere...
All refineries in the USA, or at least the lower 48 States, use the same recipes to refine two grades of gasoline.
95% of it goes into common carrier pipelines, along with various other chemicals refined from crude oil.
The other 5% goes into company owned pipelines, ie from a Chevron refinery into a Chevron pipeline, mixed with Chevron's additives in Chevron trucks and delivered to Chevron stations.
But most of the country, even at Chevron stations, you have no idea which company actually refined the base gasoline.
The additives are either delivered to the pipeline termini by trucks or railroad tanker, or in large markets it goes down the pipeline.
The additive mixing is a crude and simple as can be. It's simply pumped into the tanker trucks separately from the gasoline and relies on the mixing while filling and sloshing from the truck movement to stir together. That's where the variability in ethanol content can happen, if the guy running the pumps filling the tanker truck screws up.
Pipelines used to use moving plugs called pigs to keep products separate. Pigs were expensive, limited how the lines could be bent and required line downtime as they had to be removed at the terminal then sent back to the start by truck or train.
It was discovered that very little intermixing between products happens without the pigs, even over a couple thousand miles.
A combination of timing, measuring and chemical sensors determine when to start and stop drawing out the pure products. What does mix is called transmix.
Transmix is either sent back to the refineries or sold to power plants with turbines that can burn just about any flammable liquid.
So gasoline is partially recycled, greener than you thought, eh?
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