Gas breakdown, ionization of a gas by laser radiation, sets an upper limit on the operating pressure of pulsed CO2lasers. The breakdown threshold decreases with increasing pressure, whereas the saturation energy of the laser increases with pressure. These two competing effects lead to the prediction of a maximum operating pressure above which the energy stored in the laser cannot be extracted without initiating gas breakdown. Gas‐breakdown‐threshold measurements have been made in typical laser mixtures, and breakdown has also been observed inside the laser cavity of an atmospheric‐pressure CO2laser. Based on these measurements and previously reported saturation measurements, the upper limit for efficient use of CO2lasers is predicted to be in the range of 2–4 atm.