Exhaustive experimental investigations were carried out with a diesel genset to evaluate the potential of using CNG, hydrogen and CNG - hydrogen blend as alternative fuels under dual fuel mode of operation. A commercial genset fitted with a six cylinder, naturally aspirated water cooled diesel engine was selected for this investigation. Comparisons of performance and emission characteristics between the neat diesel and dual fuel operation have been made for different pilot fuel injection timing and different concentrations of gaseous fuels under variable load conditions. Over the entire range of engine operation, the Brake Specific Energy Consumption (BSEC) showed an increasing trend with increasing amount of gaseous fuel substitution and was higher under low load operating conditions.