Ethyl mercaptan typically is injected into commercial propane for residential, farm, industrial, or motor fuel as a warning agent. The standard concentration of 1 lb of ethyl mercaptan to 10 000 gal of liquefied petroleum gas (LPG) is used to provide a detectable odor down to a concentration in air of at least one-fifth the lower limit of combustibility. Under certain conditions ethyl mercaptan can react with materials that it contacts resulting in a loss of odor or "odor fade." LPG with insufficient odorant can be undetected if it leaks. The process of depletion of ethyl mercaptan is examined and recommendations are made to prevent odor fade or minimize its effect.