Hydrogen/carbon monoxide/natural gas mixtures are employed to simulate crude gas and purge gas. The measured laminar flame speeds of hydrogen/carbon monoxide/natural gas/air mixtures (at lean and rich conditions) show an increase trend with volumetric fraction of hydrogen or carbon monoxide and a decrease trend with volumetric fraction of natural gas. Simulation of 1-D freely propagating flame is employed to validate the measurement results, which provides useful insights for the thermal performance. Fuel mixtures of high hydrogen fraction will result in a high heat release rate, and fuel mixtures of high natural gas fraction will lead to a low heat release rate.