X rays with a mean energy of ∼50 keV produced by a flash x‐ray source have been used to preionize high‐pressure CO2laser mixtures so as to obtain uniform glow discharges. The x‐ray exposure measured in the active volume was 1–2 mR/pulse with a pulse duration of 100 nsec (FWHM) which permitted specific energy inputs of up to 300 J/l atm. Glow discharges were obtained for a variety of pressures and gas mixtures including some which were helium‐free or in which helium was replaced by argon. Further, a realistic comparison of UV and x‐ray schemes was made under sealed‐off conditions. X‐ray preionization appears to be advantageous and the resulting discharges are shown to tolerate oxygen (up to 2.6%) better. Additives such as xenon or organic compounds were not necessary for obtaining uniform glow discharges.