Hydrogen blended CNG (HCNG) is an attractive alternative to existing fossil fuels. In this study, efficacy of the HCNGs blended with various hydrogen proportions (HCNG15, HCNG20, and HCNG30) are determined. To analyze the performance of these fuels, electronic fuel injection spark ignition engine (EFI-SI engine) is considered, as this engine is commercialized, and commonly used in Thailand. A performance study for the proposed HCNGs over a wide engine speed range (1500–6000 rpm) is carried out and is compared to Gasohol-91 (E10) and pure CNG, the conventional fuels used in the country. All tests are performed with the butterfly valve partially opened at 75%. Interestingly, the specific fuel consumptions of HCNGs are less than those of pure CNG, although torque and brake power are significantly diminished. It is found that increasing the proportion of hydrogen (HCNG30) lowered the engine torque and power. It is worth noting that enrichment of hydrogen increased the brake thermal efficiency maximum of 23.75%, 23.20%, 22.31% and 21.59% for HCNG30, HCNG20, HCNG15 and CNG, respectively. For the emission aspects, HCNG fuels greatly reduced the CO, CO2 and NOx as compared to that of conventional fuels. Therefore, using these green fuels can considerably support the greenhouse gases reduction campaign. Finally, HCNG20 is recommended as a compromise alternative fuel for EFI-SI engine which is environmentally friendly.