High reliability, maintainability, and safety are expected from complex equipment and systems. The purpose of the analysis dealing with the occurrency rate and cause of defects relating to vessels' propulsion systems is to stimulate a significant step forward in eliminating the most frequent defects. When analyzing the reliability of the complex ship systems, it is necessary to define the reliability of the subsystem components, as well as the reliability of the system as a whole. The reliability of the diesel engine fuel system for one cylinder has been analyzed and so has been the reliability of the diesel engine fuel system as a whole. A higher diesel engine fuel system reliability can be obtained if the failure rate is smaller and the number of parallelly connected components of the redundant subsystems is greater. It has been proved that the reliability of the diesel engine fuel system as a whole is greater than the reliability of the diesel engine fuel system for one cylinder. In order to increase the ship's safety and her operational level, it is suggested decreasing the failure impact on the significant components of the ship propulsion system which mostly failed during their exploitation. This can be achieved by choosing significant components of much higher quality and by using a better maintenance procedure.