it depends on the application.There is a wide range of uses in the marine field..from the 1.2 horsepower,air-cooled...to the unlimited horsepower of off-shore application.
many boats use 2 cycle oil/mixed with gas engines.these are slowly being phased out in the United States and are being replaced with the more efficient and a great deal more enviroment friendly 4 strokes.
Lieutenant Minz:what type of boating do you do,and why do you ask?