||A repository of 14 gaseous organic compounds at parts-per-billion levels (7-430 ppb) in compressed gas cylinders has been established by the Environmental Protection Agency. This repository was established to provide audit materials for use in conducting performance audits to assess the accuracy and precision of Principal Organic Hazardous Constituent (POHC) measurements, especially those performed during hazardous waste trial burn tests. Five- and nine-component mixtures in a balance gas of nitrogen were prepared in aluminum cylinders for use in the performance audit program. The five-component gas cylinders contain carbon tetrachloride, chloroform, perchloroethylene, vinyl chloride, and benzene. The nine-component mixtures contain trichloroethylene, 1,2-dichloroethane, 1,2-dibromoethane, acetonitrile, trichlorofluoromethane, dichlorodifluoromethane, bromoethane, methyl ethyl ketone and 1,1,1-trichloroethane. Studies of all 14 gaseous organic compounds were performed to determine the stability of the compounds and the feasibility of using them in performance audits. Results indicate that all of the 14 compounds were adequately stable to be used as reliable audit materials. Subsequent to completion of the stability studies, several performance audits were conducted using the repository gases to assess the accuracy and precision of the volatile organic sampling-train (VOST) and bag measurement methods. The audit results indicate that laboratories can use these methods to analyze POHC with accuracy to usually within + or - 50% of the audit concentrations.