A model for catalytic combustor operation is described for a well-mixed plug-flow reactor. Heterogeneous and homogeneous reactions are considered with heat and mass transfer handled using transport coefficients. Gas velocity is allowed to vary axially and heat conduction in the catalyst bed is included. Computer solutions were obtained for axial profiles of conversion, gas and substrate temperature, velocity, and pressure. Model predictions are compared to catalytic combustion data, showing excellent agreement. Catalytic light-off, hysteresis, and homogeneous contribution are discussed. Data from a hybrid combustor developed in this laboratory are analyzed using a simplified model.