This paper presents an assessment of test data for the Sabatier CO2 Reduction Subsystem which has been selected for the Environmental Control and Life Support System (ECLSS) for Space Station Freedom (SSF). The assessment is facilitated through the application of a developed mathematical model for the subsystem. The Sabatier CO2 Reduction Subsystem is one of several subsystems included in the regenerative portion of the overall ECLSS for SSF. It provides the important function of reducing collected metabolic CO2 from the crew with H2 generated by the water electrolysis unit. (Water electrolysis primarily generates makeup O2 for the crew and for space cabin leakage.) The product water resulting from the CO2 reduction is supplied to a water recovery subsystem for further processing.The test data for the Sabatier subsystem were obtained from the comparative test (CT) program performed by the Boeing Missiles & Space Division at Huntsville, Alabama. The subsystem test data of primary interest were the performance data for the Sabatier catalytic reactor, the key functional element in the subsystem. These performance data were obtained during tests of various subsystem operations. Six different combinations of mass flow rates of CO2 and H2 were supplied to the reactor during these test operations. These different combinations of mass flow rates are indicative of different crew sizes and of different operating modes for the Sabatier subsystem and other interfaced ECLSS subsystems during flight.The mathematical model which was implemented to assess the catalytic reactor performance data was developed for the G189A generalized ECLSS computer program. The model correlates test data and analytical data for product water and methane mass flow rates within an acceptable error range.The model can be readily extended to provide greater fidelity and to include the other Sabatier subsystem components and thus provide a valuable analytical tool for support of 1) further ECLSS ground testing, 2) design decisions for flight hardware, and 3) flight operations.