At 25 degrees C and atmospheric pressure, the iodide-catalyzed decomposition of aqueous hydrogen peroxide in an undisturbed solution results in a maximum dissolved oxygen concentration of 0.12 M, or about 100 times the equilibrium solubility. At this concentration loss of gas occurs by homogeneous nucleation of bubbles. The supersaturation is readily destroyed by agitation or by sonication. As the external pressure is increased, the maximum attainable oxygen concentration increases linearly, reaching 0.18 M at 50 atm. In a plot of-dissolved gas concentration versus external pressure, the supersaturation line is parallel to the Henry’s law (saturation) line. The maximum supersaturation concentration at elevated pressure is independent of the nature of the pressurizing gas. While the pressure dependence of the supersaturation limit caa be understood in terms of existing nucleation theory, the theory fails in attempts to calculate that limit quantitatively.