An important consideration in building large‐volume gas amplifiers, given the pulse duration, is the maximum output intensity which the amplifying medium can support. We consider this problem in detail for CO2lasers to be used in laser fusion experiments. We describe a new means of computing properties of the electron distribution function using a Monte Carlo model, and compare computations by this method with a more common Laplace transform technique. The physics of the models is carefully considered, and the previously ignored effect of Penning ionization is shown to be of potential importance. The computations strongly suggest that for a 1.3‐nsec pulse at 10.6 &mgr;, using conventional pumping techniques, an intensity of 2.3 × 109W/cm2results in less than a 10% energy propagation loss, and that an intensity of 3 × 109W/cm2results in more than a 10% loss.