Seeing that you want to sell the fuel from your store and want to stay with Byron then I'd suggest getting their [link=http://www.byronfuels.com/pages/products.html#chart_anchor]Premium Sport "Traditional"[/link] blend which has 20% oil as an 80/20 synthetic/castor mix. Byron mixes fuel by weight so their "20%" oil is the equivalent of 16% mixed by volume which is just barely into an acceptable safe range.