A model of the homogenous CO2 laser plasma is presented which can be used to describe the efficiency of laser operation for both the DC and the RF- discharge. As laser gas a mixture of CO2, N2, and He with an admixture of Xe was used. To simplify the calculations the distribution of the electron energy was considered to be a Maxwellian one which makes it possible to avoid the solution of Boltzmann's equation. In addition only the most important collision cross sections were used, namely the cross sections for excitation of vibrational modes in CO2 and N2, for attach-ment and electronic excitation of CO2, for ionisation of CO2, N2, and Xe, for elastic collisions and for momentum transfer. Under these assumptions the energy and the particle density balances for electrons can be put up. As a result the energy transfer to the different levels in CO2 and N2 and the electron density can be calculated which can be used to estimate the efficiency of the conversion from electrical power to laser radiation. The evaluation of this model showes that the efficiency of the RF- discharge is a little bit higher than that of the DC- discharge which is mainly due to the more favourable conditions for ionisation in the RF- discharge. The admixture of xenon causes a sig-nificant increase of the electron density for a given value of E/N which raises the efficiency considerably.