I want fuel that works in the maximum number of my engines. I don't want to take 4 planes to the field, and have to lug 4 bottles of fuel to go with them. I use 15% Omega 50/50 castor/synthetic on everything except my .049/.061 Norvels, which get 25% Byron all castor. So the gallon bottle fuels my .074-.74s (I don't have anything larger, but when I do, it has to handle that fuel, or I won't bother) and the quart fuels the 1/2a's.