a friend of mine used to haul gasoline from the refinery to the stations.I am using the term "fuel blender" to indicate the blending process at the refinery but also to broadly define whoever is finishing the gasoline. I didn't want to say refiner since the fuel might be further blended after refinery ie terminal or splash blended at the station. In fact, by adding anything to the fuel, you are now the blender.
he told me that each brand of gasoline had a specific "treatment package" that was to be dropped into the tanker before he hooked up the hose to fill the tanks. The tankers have several tanks separated so he can haul 650 gallons, or... IIRC, his tanker had 4 partitions of different sizes.
He told me, that the refinery puts out one grade of gas only, and that the ethanol that he has to "blend in" to a specific tank is what causes that tank to contain "87" or '91' or whatever. And that gas the refinery has does NOT have any additives at all.... the tank truck driver is responsible for that job..... He was a trainer for many years, and said the law requires the new tanker drivers to have six months of 'OJT' before they are released to drive on their own...
IIRC, this has been a couple of years now, he said the refinery is 85 Octane, and the driver has to blend in whatever is required to raise the octane. So, that 87 octane we get has 10%, more or less, Ethanol in it.
the higher grades have even more Ethanol, so the octane can be raised to 91, etc.