Human error is a crucial factor in the shipping industry and not to mention numerous human errors occur during the maintenance procedures of marine engines. Determination of human error probabilities (HEPs) is important to reduce the human errors and prevent the accidents. Nevertheless, determination of HEPs in the maintenance procedures of marine engines has not been given desired attention. The aim of this study is to determine the HEPs for the maintenance procedures of the marine engines to minimize the human errors and preclude accidents from the shipping industry. The Success Likelihood Index Method is used to determine the HEPs due to the unavailability of human error data for maintenance procedures of marine engines. The results showed that among the 43 considered activities in this study, inspection and overhauls piston/piston rings have the lowest HEP meaning it has a lower consequence for accidents. On the other hand, fuel and lubricating oil filters pressure difference checking and renews filter elements activity have the highest HEP indicating it has high chances for accidents.