Saturation concentrations of dissolved oxygen in an aqueous-H2SO4 medium at 25 degrees C were measured in pulse radiolytic competition-kinetics experiments, wherein the H atom (H-. radical) was generated in situ by a 50-ns electron pulse, and, subsequently, the propensity of its reactions with O-2 and another solute of choice were compared on a microsecond time scale. Such direct chemical estimations reveal that an oxygen concentration of similar to 1.28 mM at pH 2 steadily decreases to similar to 310 mu M at a H2SO4 concentration of similar to 14 M, and it now provides a quantitative picture for evaluating oxidative stress in high acidity.