PURPOSE: To provide an oil tanker propulsion system for safe and economical combined diesel/electric propulsion capable of preventing unnavigableness even when a main engine is stopped due to an emergent failure, also coping with an emergency so as to prevent the occurrence of a dead time during propulsion and cargo handling, and moreover operating the propulsion and cargo handling without useless time.

CONSTITUTION: This system is provided with a diesel main engine 1 for driving a variable pitch propeller 6 via a main shaft 8, a gearing 9 inserted into the main shaft 8, single or plural auxiliary diesel generators 7 for driving the main shaft 8 by inputting output into an electric propulsion motor 2 via a switch box 10, a frequency converting thyristor 5, and interlocks 11a and 11b, and a cargo oil pump driving circuit for inputting the output of the frequency converting thyristor 5 into a motor-driven cargo oil pump 3 via the interlock 11b.