Originally Posted by Zat_Zuma

What I learned today from the resident lab tech is that most ethanol blended gasolines octane ratings are mostly based on theory.

What it means is that a fuel; octane motor tested in a lab (R+M/2), can be calculated for a retail pump octane with the addition of ethanol. Ethanol octane rating is 130 octane. Sooo lets say for example of a base fuel is lab tested to be a 89 octane fuel. By adding "up to 10% Ethanol" a company can calculate the octane to 91 and sell it as a 91 octane fuel at the pump without any lab testing.

So is it really a true 91 or 94 octane fuel? Probably not and depending on the math calculations and Ethanol addition %, one can not be sure what % Ethanol is added or the true octane rating of the fuel.

There are changes coming in Fall of 2012 mandated by the govt, so I will check into this next.