Because its made for use at high altitudes, it has a different specific gravity. If you run this fuel you will need to adjust your float levels. This is fine if you run it continuously BUT if you put a tank full in your car, drive far enough to use all or most and then fill up with pump gas, the car will run like crap until you readjust the float levels. Been there, done that. It wasn't worth the hassle. You can run Shell high test - apparently its the only fuel on the market that does not (yet) have ethanol in it.