A method and composition for identifying chemically tagged petroleum products can be achieved by adding one or more chemicals to a selected petroleum product wherein the chemical is immune to extraction from the petroleum product by conventional inexpensive absorbents, cannot be removed by extraction with acids, bases, or immiscible solvents, cannot be easily oxidized, reduced or reacted with common agents, is difficult to disguise by masking with other agents, has a low polarity, and has a boiling point in the range of the petroleum product the chemical is being added to. The presence of the chemical is determined by using ion mobility spectroscopy.