Blended fuel octane rating

[jmann]

Simple question, if I have half a tank (10 gallons) of 93 octane and I fill it the rest of the way with 89 octane, will the result be the same as using 91 octane gas? Logic to me says yes but I want to know if anyone actually knows the answer to this question.

TIA

[hannibal]

You are correct.

In fact, gas stations do not stock mid grade gasoline. It is simply a blend of regular and premium that's mixed as it's dispensed. In areas with 87 and 91 octane, it's a 1:1 ratio to make 89. Outside of the west coast where you usually find 87 and 93 octane, its a 2:1 mix.