100 low-lead is a common aviation fuel. Most small aircraft use it. Piston engines generally use that, while jets of course use jet fuel. There are piston engine that run on jet fuel (often diesel), but they are rare and just starting to come out.

I don't know about sea planes though. My guess is they use lead because that is the best educated guess.

edit: others are claiming that these planes are mostly turboprops which would then use lead free jet fuel.