The plasma kinetics of sealed off room temperature CO lasers have been investigated by measuring the gain, electron density, and discharge voltage in various gas mixtures which are used for 'such lasers. In certain cases the positive ion spectrum has also been studied. This has led to an understanding of the effects of Xe, O2 N2, H2 and CO2 on the plasma kinetics of CO lasers, and these effects can be broadly divided into three classes, (a) The additives which primarily alter the electron kinetics and change the electron impact excitation rates to CO, these are also usually found to alter the positive ion spectrum, eg Xe, O2. (b) Those additives which are important in altering the vibrational kinetics by changing the V-V-T near resonant exchange rate, eg N2. (c) Those additives which alter the V-T relaxation rate and hence affect the vibrational kinetics of CO, eg H2. In general in a working laser all three of the above processes must be considered. By understanding how each of the gases mentioned earlier can affect the CO laser plasma, high power, high efficiency single line and multiline CO lasers have been produced.