Since an outboard engine is like any other type of engine, it requires a range of different fluids to keep it running properly. The different types of outboard motors run in different ways but all of them require gasoline to create energy and oil to lubricate the inner workings of the engine. It is not possible to keep a boat running with just one of these fluids.
For some types of boats, the oil and the gasoline are mixed together and flow together through the engine. These outboard motors require a larger supply of oil over time since they constantly have to maintain the same ratio of oil to gasoline. Other outboards have a separate area where boat motor oil can be added so that the engine can use it easily.