Advances in renewable energy sources and impact of green house gases on climate change have led intense research in the area of renewable energy for transport and power generation sectors. All over the world gaseous fuels have gained momentum as an ideal alternative fuel for meeting future energy needs. Hydrogen enriched compressed natural gas (HCNG) may be considered as an alternative automotive fuel which does not require any major modification in the existing CNG engine and infrastructure. Several studies of HCNG fuel were reported on small and light duty engines / vehicles, but limited reports are available on heavy duty engines. In this study, experimental investigations were carried out on a 6 cylinder heavy duty CNG engine which has been optimized for 18 percent HCNG. Initial performance of the engine on HCNG was compared vis-à-vis CNG and, thereafter, the engine was subjected to endurance test as per BIS 10000 norms for 100 hours (severe cycle) with HCNG. Performance of the engine was monitored at every 10 hours interval and at the end of the endurance cycle performance of the engine was assessed as per European Transient Cycle (ETC) with emission measurements before and after catalytic converter and reported.It was observed from the test results that HCNG has shown reduction of CO, THC & CH4 emissions by 39, 25 & 25 percent respectively and NOx increased by 32 percent as compared to CNG. The average power output was nearly same with HCNG at the end of the endurance test. Further, the results after the endurance test showed increase in CO emission whereas THC, CH4, NOx & CO2 emissions reduced further but were well below Euro-IV limits. The conversion efficiency of catalytic converter was about 95-97 percent at the end of the durability test. There has been no significant change in Specific Energy Consumption (SEC) at the end of the endurance test. The performance of the engine lubricant at the end of the endurance test with HCNG has also shown no significant changes in viscosity, TBN and wear elements compared to fresh lubricant.