Supercritical water oxidation (SCWO) is currently being developed as a means of destroying resilient, highly toxic waste, such as halogenated hydrocarbons (e.g. polychlorinated biphenyls, PCBs) and the hydrolyzate from chemical agents. The advantages offered by SCWO over incineration, for example, include closed cycle operation and very high destruction efficiencies. The latter are achieved by employing very aggressive oxidizing conditions that are obtained by maintaining a high oxygen fugacity in the system and by operating at elevated temperatures (up to 650 degreesC). These conditions are also extraordinarily corrosive towards common structural materials, such as nickel-based alloys and ceramics. This paper reviews some of the properties that define the corrosiveness of SCWO media towards common structural materials and identifies issues that must be resolved before this technology becomes a practical reality. In particular, we show that it is now possible to measure pH and polarization data at temperatures well above the critical temperature, even though the density and viscosity of the medium are more characteristic of a dense gas than they are of water under ambient conditions.