This paper presents numerical analysis of efficiencies and non-measured operating parameters for the marine two-stroke slow speed turbocharged diesel engine 6S50MC MAN B&W with direct fuel injection. Numerical analysis was based on a measurement set performed at different engine loads. Calculated efficiencies were mechanical, indicated and effective efficiency, while the calculated important operating parameters were power of engine mechanical losses, mean effective pressure, effective engine torque and specific effective fuel consumption. Engine load was presented in percentage of maximum continuous rating (MCR). The highest engine mechanical efficiency of 94.52 % was obtained at the highest engine load, while the highest engine effective efficiency of 49.34 % was obtained at the engine load 75 % of MCR. Available engine effective torque was from 267380 Nm on the lowest up to 643594 Nm on the highest engine load, while effective fuel consumption was between 171.18 g/kWh and 186.83 g/kWh.