You do not HAVE to use after-run oil, but in my opinion its a REAL good idea.

Some of the better fuels have some very good additive packages in them. With a little care, and the right engine, you can get away with not oiling up after every flying session... and sometimes you are safe for a good deal of time.

My post-flying ritual usually includes a few drops of after-run oil in the carb. For storage more than a few weeks, I definately oil-up the engine.

Note in their statement, they say no petrolium based oil. That is important.

I personally use and recommend either air tool oil or marvel mystery oil.