Presents a theoretical model of a transversely excited CW CO₂ laser. The laser rate equations as well as the basic hydrodynamic and thermodynamic equations have been used to describe the whole laser system. The spatial distributions of small signal gain and saturation intensity along the gas flow direction have been calculated for a given set of initial conditions, namely, pumping rate, gas mixture, total pressure, gas temperature and gas flow velocity. The dependence of laser output power on discharge and flow parameters is in good agreement with the experimental data, confirming the usefulness of this model for understanding laser performance.