Abstract: A fuel gas blending system for internal combustion engines combines two or more gas streams to achieve a blended fuel gas having a suitable heating value (HV) for a given engine. A relatively high HV gas, for example gas produced from an oil and/or gas well, or containerized propane, is blended with a relatively low HV gas, for example nitrogen. The blended gas achieves a fuel gas with a suitable HV. Suitable means for combining the gas streams, analyzing the blended gas stream for HV and other properties, and adjusting the blend as needed are all provided. The system permits use of available gaseous fuel sources, even if not suitable in an unblended state, to efficiently fuel internal combustion engines.