I am not ethanol insider but I can answer some of your questions. Not all gas is refined to 84 octane but the refineries do not want to refine it any further than they have to. If they want a finished product of 87 octane they will refine the gas to 84 and than blend the ethanol with it to make 87 octane. In most states 87 is the minimum octane rating that they can sell so that is why a lot of gas is refined to 84 octane. If they want 89 octane they can refine the gas to 86 and than blend 10% ethanol with it to get to 89 octane or they can just refine it longer until it is 89 octane.

All the gas sold does not have ethanol in it. I am not sure on the exact % of gas that is blended with ethanol, but it is over 90% and probable closer to 95% now. In our area some of the gas stations will advertise ethanol free gas for small engines and collector cars. They charge a higher price for the non oxygenated gas. In MN it is illegal to put non oxygenated gas in newer cars. I am not sure on what age the car has to be to put non oxygenated fuel in it. It might be illegal to use non oxygenated gas in new cars but there is really no enforcement of that law.

A lot of time the 91 octane is non oxygenated gas and they sell it as premium and charge plenty for it. There is also 91 octane premium gas that does contain ethanol but the refineries would than just have to refine it to 88 octane and than blend the ethanol with it. To get to 91 octane they will just have to refine it longer.