There's a lot of theories on this myself have yet to get straight answer low ethenal or no is best depends on compression ration one weather u need premium safe bet is use it. But I have ask people what I should do and they tell me to make sure u get no ethenal even though I've been w them when they fill up at the car pump. What I do is fill at normal station that I know has 5% and put in stabil ethanol reducer some also use cfoam. Hope that helps