what's the difference between gas?

Gas is measured by octane rating which is the rate it burns. So the longer it takes for the gas to burn the higher the octane rating. If your car requires a 87 octane and you were to put a higher grade in it your cars computer would notice the slower burn time and would adjust to that burn time. So buying higher grade fuel is not better. Because your computer will adjust and it will be the same as if you were to put regular gas in. Also buying the mid-grade gas is a horrible deal I guess to because their just mixing 2 parts regular and 1 part premium. You would save more money if you were to put 5 gallons premium and 10 gallons regular. There is the ethanol option now that is more clean burning then gas but it burns allot faster then gas  and there is not nearly as much energy as compared to gas. So you would be burning more ethanol then gas, even though its cheaper your using it faster so not the best buy.