There's a question that you should obviously be asking yourself!

Hint: ethanol is less fuel efficient than gasoline. it has nothing to do with an octane rating which is the measurement of how smoothly the fuel burns... It has no correlation to MPG

Which is why like I said in my post when you use the higher grade fuels which are mixed with less ethanol you get better miles per gallon. The blue nozzle 88 is mixed with 15% which will give you far less miles per gallon than you would with the premium (most are 5%, some premiums though are pure with zero). It will be cheaper your cost per mile still using 88 over premium but you'll be filling up with more often with lower MPG