The factors that govern the performance of activated carbons for the control of evaporative emissions in an automobile are discussed. First, the physical properties that affect its ability to store and subsequently release hydrocarbon vapors are considered. Secondly, accelerated test procedures are described to evaluate the adsorptive stability of the carbon. The results of these tests are discussed and related to long-term performance. Finally, the adsorption-desorption principles applicable to evaporative loss control are outlined. Guidelines are presented for the application of these factors to the design of effective systems. It is concluded that activated carbons commercially available at present, can meet the capacity and durability requirements of the automobile environment.