The final paper explains the fuel system of marine diesel engines. Liquid and, more recently, gaseous fuels are used as propulsion fuel for ship propulsion systems. Liquid fuels can be petroleum products or can be obtained artificially from solid fuels or organic substances. Gaseous fuels can be natural, such as natural gas, and are also obtained artificially. With the development of maritime and marine engines, there is a greater demand for marine fuel Liquid fuels are still the most important and most common in the application of propulsion and auxiliary machines. Large marine diesel engines most often use heavy fuels for propulsion because they are cheaper than diesel fuels. The fuel system on board consists of different subsystems that are interconnected. The main goal of a marine fuel system is to prepare and provide a sufficient amount of fuel. The ship's system consists of the constitution of loading and transfer of fuel, the constitution of fuel storage, the constitution of fuel purification and the system of fuel supply and injection.