I see where several Opti owners have replied. I to have a Optimax, and Optimax oil is all I use. My old boat had a Merc Black Max on it and I used the Quicksilver oil in it. I called Mercury when I got my Opti, and they strongly urged me to use only the Opti oil. I'm in central Ky. and Kaylors Marine sells it in bulk for $17.00 a gallon. The Opti's are oil injected at 25:1, -vs- the older Mercs that are 50:1. Just my opinion but I would only use the Optimax oil.