Fire behaviors of three gaseous hydrocarbon fuels were experimentally measured and compared at two different altitudes (Lhasa city, 64 kPa at an altitude of 3650 m; Hefei city, 100 kPa at an altitude of 50 m). The heat release rates were calculated through a simplified thermochemistry based on the measured concentrations of O-2 and CO2 in the exhaust duct, then the combustion efficiencies and the radiation fractions were compared at the two altitudes. The heat release rates and combustion efficiencies were higher at lower pressure, and the overall temperatures of methane fires rose at a lower pressure. The radiative heat fluxes and radiation fractions at a low pressure were smaller than those at a normal pressure, while the smoke transmittances of acetylene fires at a low pressure were higher.