Research was initiated due to increased concern over trace contaminant gas build-up in an enclosed atmosphere of a spacecraft for long duration space flights. A gas mixture simulating conditions on long duration space missions must be created in order to test trace contaminant control hardware. A trace contaminant data base was developed from the gas, lithium hydroxide, and charcoal samples collected on shuttle missions. This paper analyzes the contaminants collected from individual space shuttle missions in order to provide a model contaminant gas mixture. A model trace contaminant gas mixture containing 14 compounds was chosen with the aid of a FORTRAN computer program. The contaminants were chosen based on their distribution between chemical and toxicological categories, frequency of occurrence, and the worst case concentration. One contaminant, benzene, is a systemic poison, another, chlorotrifluoroethene, an asphyxiant, while the rest of the contaminants are evenly divided between CNS depressants and irritants. This contaminant model gas mixture can be used to test trace contaminant control hardware for an enclosed spacecraft environment.