I recommend always using premium gasoline- the highest octane available at the gas pump. Then, it is best to use synthetic 2 stroke motor oil [ non sysnthetic creates more sludge] . Dino at Screaming Roo says 50:1 mix which minimizes sludge and is really adequate for lubrication and cooling. I have seen recommendations ranging from 16:1 to 100:1. From my experience running too much oil hurts more than it helps. I have had stock exhaust pipes plug solid with from using too much oil. And I have seen engines gummed up from too heavy of a mix. Dino of Screaming Roo would be the expert. He has taken apart and put together these 2 stroke bicycle motors more times in one day than the majority of us will ever do in a lifetime. If he says 50:1 that would be the proper ratio. However, I like to play it safe also. So I typically go with 2.5 ounces of Amsoil Dominator [available at link] per gallon of premium gasoline, which equals around 40:1 ratio. Of course most of my work is on new engines, that have not been broken in at all. So, 50:1 is the ticket. Finally the icing on the cake , I pick up 104 octane boost [Walmart] as these engines really love octane.Note : no more than one ounce [shot glass] of 104 octane per gallon or the engine may not run if you use too much.Summary: Highest octane premium fuels/ Amsoil 2 stroke/ 104 octane boost.