A simple approach is described for the calculation of both the lean- and rich-flammability limits of fuel/diluent mixtures in air for a wide range of initial temperatures, based only on a knowledge of the flammability limit of the pure fuel in air at atmospheric temperature and pressure. Fuel/diluent mixtures that include the fuels methane, ethylene, ethane, propane, butane, carbon monoxide and hydrogen, and the diluents nitrogen, carbon dioxide, helium and argon, were considered. Good agreement was shown to exist between predicted values of the lean- and rich-flammability limits, and the corresponding available experimental values.