I use 87 most of the time. I have run premium a few times and it seems to add 1 or 2 MPG but not enough to warrant its use for the price difference. I to have came accross a couple stations here in MN that offer the 89 octane for the same price. I always put it in when that is the case in all my vehicles. Though I don't know if I gain anything. Ethonal does us no favors for power or Fuel Efficiency. I use Oxy free fuel in all of my small engines and boat. Too bad is wasn't legal in my EcoBoost cause I would use it in there as well.