Motul 4T 4 Stroke 3100 GOLD 10W40 Technosynese Oil 1L
Your 4 stroke jet ski should not use oil unless there is a problem.
Check the dip stick every few rides. The engine should be started and run very briefly then rested for a few minutes to get an accurate dip stick reading.
The oil should be changed at least once a year or every 25-50 hours (model dependant). Send us a question if in doubt!