Morgan fuels typically have 17 or 18% oil in'em. Can't quite remember which, but no matter. 128 oz in a gallon of fuel, and we'd like to bring it up to 20-22% total oil, typically. If you're flying only "normal size" engines, then 20% is entirely adequate (actually, so probably is what's in there to begin with, but this is about insurance, not current needs). If you fly anything 1/2a, 21 or 22% would likely be better. Since we're looking to add 3-4% total oil (.03 x 128 = 3.84), 4 oz would be about right for a gallon, or 1 oz to each quart.

J