By measuring the oxygen consumption during dissolution of irradiated solid compounds in water with different oxygen concentrations, the ratio of the radical-oxygen and radical-radical reaction rates can be obtained. In a series of six compounds with molecular weights from 75 to 504 the ratio of the reaction rates increased from 2–3 to over 20. The increasing dominance of the radical-oxygen reaction rate over the radical-radical one at increasing molecular size probably depends on a combination of diffusion and steric factors. The radical concentration of the irradiated solid compound can be evaluated by a linear extrapolation of the oxygen consumption to infinite oxygen concentration in the dissolution water. The radiation-induced radical yields, measured in this manner, agree well with results obtained by ESR investigations.