Atomic oxygen density profiles in the 90–140 km altitude region have been obtained by analyzing the radiation intensity of chemiluminous nitric oxide trails deposited by rockets into the upper atmosphere. The trails consist of a very bright headglow and a dimmer afterglow. The headglow is believed to originate in the mixing zone around the NO jet expanding into the atmosphere. A gasdynamic model is given defining the reaction volume and time for the NO-O reaction in the headglow. Oxygen atom densities are evaluated by applying the gasdynamic model to the radiation intensity of the headglow. The resulting altitude profiles indicate maximum oxygen atom densities in the 103–107 km region.