The aim of this work is to study the combustion and gaseous emissions characteristics of a diesel engine dual-fueled with natural gas at different operating conditions (light to full load) for generator application. The electromechanical system was composed of a commercially available 18 liter, 6-cylinder diesel engine, coupled with the generator rated at 600 kWe at full-load. The flow of natural gas was electronically controlled using a throttle valve, and was inducted in the intake manifold before being introduced into the combustion chambers. Gaseous emissions of carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) were measured under both diesel and dual fuel operations at different loads. This work also presents the effects of diesel oxidation catalyst to reduce HC and CO emissions under dual fuel operation. At each operating load, gas percentage was increased with corresponding decrease in diesel pilot while maintaining the same power output. The engine cylinder head was modified to accommodate a piezoelectric pressure transducer in each cylinder to record incylinder pressure data for combustion analyses. Measured incylinder pressure, exhaust emissions and other relevant engine parameters, e.g. temperatures and pressures at various locations, were then used to identify the limiting parameters on gas induction at various loads. As expected, NOx emissions are reduced under dual fuel operation compared to diesel operation. The results also showed that cyclic variability, cylinder-to-cylinder variations in the combustion process, and HC and CO emissions limited the gas induction at light loads. At higher loads, exhaust gas temperature limited the percentage of gaseous fuel under dual fuel operation.