I've worked at both the refining and retail side of automotive fuel. Currently in my neck of the woods: Low Grade w/Ethanol starts out as unbranded 84 octane and is blended at the terminal 9 parts gas / 1 part ethanol to create 87 octane High Grade w/Ethanol starts out as unbranded 91 octane and is blended at the terminal 9 parts gas / 1 part ethanol to create 93 octane Mid Grade is usually blended at the Dispenser 66% 87 octane / 34% 93 octane. (I've programed dispensers). The few stations that still have a mid grade underground tank will blend at the terminals. (Check the gas station's tank farm for blue caps). Any E0 fuels are blended at the terminals with 84 E0 and 91 E0. A few stations will blend E-85 with low grade E10 for 88 E15.