Go with a good marine grade oil NMMA FC-W certified oil. From talking to my mechanic/dealer regular oil does not have the same corrosion protection as the marine grade oil. I have a 4hp Tohatsu and I bought a bottle of 10W-30 QuickSilver Performance 4-Stroke Oil for it's first oil change. If I remember right these little motors only hold about 15 Fluid Ounces, so 1 bottle/quart is good for about 2 oil changes maybe. Regular oil would work but I think it would shorten the life of your motor in the long run due to it not having the corrosion inhibitors of quality marine oil.