Representative low-Btu gas mixtures derived from coal are presented and simplified, resulting in synthetic low-Btu gas mixtures composed of H2, CO, CH" N2, and C02. Mine-atmosphere flammability data are applied to the synthetic mixtures 10 produce flammability limits at one atmosphere and 77 "F. Twocomponent synthetic mixtures of CH, and an inert gas are shown to be not suitable for certain combustion experiments requiring low-Btu gases.