I got tired of smoke oi prices, even from the local Copperstate Petroleum. I ended up buying a case of 4 gallons of CSP contrete form release oil at $14/gallon. I find the single gallon jugs easier to work with, but it is also available in 5-gal pails at $54 ($13.50/gal). CSP smoke oil is $85 for the 5-gal pail ($17/gal). The tech at CSP said the formula is "very similar" to CSP aviation smoke oil.
My experience is that it gives a very good plume, but maybe (?) leaves a little more on the bottom of the plane. In the long run, since I go through only about 10 gal/year, the cost difference is not significant, but the form oil is much easier to find.
Andy Elliott, CFI, RV-8, N303RV
Flight Reviews, Dynamic Prop Balancing
KFFZ, Mesa, AZ
2021 Dues Paid