Like he said it varies area by area. I have found that if i drive any of my cars, which all require 91 octane or higher on the highway for a long distance and i mix the gas which i have done for years as long as that is what i am left with ( the lower octane) i dont have any issues. However if you stomp on the gas it does not seem that powerful. I did that with a Mercedes and i thought the car was going to blow up. My personal cars all but one are all over a 100K and are still going strong. Do what you are comfortable with.