An experimental technique for the measurement of the rate of formation and removal of atomic oxygen in an active glow discharge is described. The concentration of atomic oxygen was monitored with a mass spectrometer by sampling the gases flowing through the discharge. The rate of removal of oxygen atoms was found to be first order in atomic oxygen and 10 to 100 times faster than the corresponding recombination rate in the afterglow region. The measured rates of atom production are in agreement with those calculated by assuming electron impact dissociation of ground state molecular oxygen. The atoms are removed by a wall recombination process.The ability of trace amounts of certain gases to enhance significantly the extent of dissociation in an electric discharge in oxygen has been studied. Only those added gases which contain a hydrogen or nitrogen atom are effective in enhancing the yield of atomic oxygen. For each hydrogen atom introduced into the oxygen stream about 300 extra oxygen atoms could be produced. This 'catalytic' effect is shown to be due to a marked decrease in the rate of recombination of O-atoms at the walls of the discharge tube. Whatever small change that occurs in the rate of O-atom production can be easily accounted for by a change in the energy distribution of the electrons in the discharge due to the effect of the additives.