The ever increasing demand of fuels for vehicles can only be met by use of alternate fuels like Compressed Natural Gas (CNG) and Hydrogen (H2). The 18 percent hydrogen enriched CNG fuel referred to as HCNG has the potential to lower emissions and is considered to be the first step towards promotion of a Hydrogen economy. While, automotive industry matures up with the usage of new engines, lubricant manufacturers are also moving on to the next stage by formulating oils to be used in gas engines such as CNG, HCNG etc.This paper presents the evaluation of gas engine oil on 6-cylinder heavy duty CNG engine using HCNG. The six cylinder engine was chosen due to its importance for urban bus transportation. The engine was optimized for using HCNG fuel. Initial performance of the engine using HCNG was compared vis-à-vis CNG and, thereafter, the engine was subjected to endurance test of 500 hours as per 8 mode engine simulated driving cycle. It has been observed that HCNG shows reduction of CO, THC and CH4 emissions and NOx emissions increased as compared to CNG. However, these values meet the Euro IV emission norms. Oil sampling and analysis were undertaken after completion of every 100 hrs. Also, performance and emission characteristics of the engine were analyzed after completion of every 100 hours as per European Transient Cycle (ETC).The performance parameters of the engine lubricant such as kinematic viscosity @ 40°C, kinematic viscosity @ 100°C, viscosity index and TBN over the complete endurance test of 500 hrs were within the permissible limits. Wear elements like Fe, Al, Sn, Cr, Si, Pb, Ag etc. were within limits over the period of endurance test of 500 hrs. Specific fuel consumption (SFC) measurements were consistent at all the 8 modes of engine simulated driving cycle. Test results indicates that over the period of endurance test of 500 hrs with HCNG, all the major exhaust emissions species such as CO, THC, CH4 and NOx emissions were lower than the Euro IV emission norms for the heavy duty engines and there were no significant changes in the CO2 values. The study shows that the engine oil can be used for long drain application.