I recently changed the oil in our Onan gas generator. Went to the local onan dealer and they sold me Valvoline, All Fleet Plus Heavy Duty Diesel Oil. Because of our location, Manitoba Canada, They recommended SAE 10W-30. I questioned the use of Oil marked "Diesel", but was assured this was the correct oil for my generator. On the back of the container it states "for turbo, diesel and gasoline engines". Hope this helps answer your question