main thing is that supposedly, according to mercury, the DFI oil has a better additive package that produces less carbon, something that has been an issue in the optimax motors. Ive been running DFI oil plus the recommended 1 oz of merc quickleen (again, may the spellcheckers rot in hades – I give up on this word) per 5 gallons of gas. If you buy it in bulk it is not so bad, would not buy it at wally world. Ive been thinking about a 55 gallon drum myself as much as we have been burning. Been through 5 gallons in 4 months now.2008 Pantera Classic2014 Mercury Pro XS 200