Just curious if any other people out there are shelling out the extra $ for 91 octane fuel? My prius hasn't had anything but 91 and my theory is that it will run better and possibly use less fuel. I could be wrong and don't really know if it matters at all. I noticed at idle when I'm waiting for a red light the car almost shakes a bit sometimes as if the car was spitting exhaust out intermittantly. It only happens once in awhile but I'm curious if anyone else is using the 91 octane fuel and getting the same behavior. Does anyone know if this is normal? This car is so cool that nearly everyone I talk to is interested in it, I love my greenmachine.