It depends on your engine. A 66cc HT with good port work, high compression head, good expansion chamber exhaust, etc. may have issues with detonation, even with 91 octane unleaded. I am running a CR Machine Stage 2 engine with 6 cc combustion chamber and sbp chamber and it requires fuel with an octane rating of higher than 91. I'm not sure exactly what octane level is the lowest that would be sufficient, but the Vp 110 eliminated the detonation problems I was having. Unless you have done extensive modification to your engine, you could probably run pump gas with no problems. The 5 gallon can I bought was $50+. It does smell great when it burns, though. Nothing like the aroma of some spent Vp110 in the morning!