Abstract: Disclosed is a device and a method for measuring the partial pressure of oxidizing species in a liquid. A metal or incompletely oxidized metal oxide which is susceptible to anodic oxidation and which forms an oxide having a Pilling-Bedworth ratio greater than one is placed in the liquid. The oxide formed on the metal is confined and the pressure of the confined oxide is measured. That pressure is a known function of the concentration of oxidizing species in the liquid. The device is calibrated in liquids of known oxygen content to establish the relationship between oxide content and pressure.