Maritime type of classification is used for fuel oils

Maritime
In the maritime field another type of classification is used for fuel oils:
• MGO (Marine gasoil) - roughly equivalent to No. 2 fuel oil, made from distillate only
• MDO (Marine diesel oil) - A blend of gasoil and heavy fuel oil
• IFO (Intermediate fuel oil) A blend of gasoil and heavy fuel oil, with less gasoil than marine diesel oil
• MFO (Medium fuel oil) - A blend of gasoil and heavy fuel oil, with less gasoil than intermediate fuel oil
• HFO (Heavy fuel oil) - Pure or nearly pure residual oil, roughly equivalent to No. 6 fuel oil
Marine diesel oil contains some heavy fuel oil, unlike regular diesels. Also, marine fuel oils sometimes contain waste products such as used motor oil.