A comprehensive EPA emission test analysis program has been developed to determine the nature and relative significance of test variability and to provide consistent evaluation of the performance of catalytic converters. This includes real-time recordings of emission concentrations and mass rates, catalytic converter efficiencies, and air-fuel ratio. Mass accumulations are printed out during the test at the end of each test mode. Test results and analysis of repeatability are summarized on-site immediately following the test. Simplified relationships between gas concentrations and engines variables have been developed.