The potential of sub- and supercritical water as reaction medium for the partial oxidation of propane to oxygen-functionalised hydrocarbons (oxygenates) was studied at temperatures from 633 to 693 K and pressures from 16.7 to 28 MPa in batch and continuous runs with synthetic air as oxidant. Additional experiments with heterogeneous catalysts (Carulite 300(R), MnO2, Co2O3, MnO2-Co2O3, MoO3, all supported on gamma -alumina) provided information about behaviour of oxidic materials at hydrothermal conditions. The properties of fresh and spent catalysts were characterised by several standard methods (BET, ICP, XRD, SEM, XPS). The influence of reaction parameters like temperature, pressure, density, residence time, and feed composition on conversion and selectivities was examined. Transition of reaction mixture from sub- to supercritical region shows significant influence on propane and oxygen conversion rates, due to homogenisation of reaction mixture and improved mass transfer. Influence of catalyst materials is comparatively small. Total sum of oxygenates selectivities reached 15% at 90% propane conversion and methanol was the mainly formed oxygenate. (C) 2001 Elsevier Science B.V. All rights reserved.