Partial oxidation of bitumen was examined in supercritical water from 653 to 723 K at a water/oil ratio from 0 to 3 and up to 5.1 MPa of initial air pressure. The contents in the reactor were separated into water rich phase and oil rich phase. Most of oxygen was quickly consumed within 30 min and the main gases produced were CO, CO2 and methane. The low temperature gave higher CO/(CO + CO2) ratio and suppressed coke formation. The amount of total gas tended to decrease and the ratio of CO/(CO + CO2) increased about two times by the increase in water/oil ratio from 0.5 to 3. The high water/oil ratio was preferred for selective partial oxidation to produce CO, which means that the effect of the enhancement of partial oxidation by supercritical water was probably larger than that of CO oxidation by water and water gas shift reaction. The increase in initial air pressure increased the amount of CO and CO2 and decreased the ratio of CO/(CO + CO2). The total oxidation route was enhanced under high air pressure. (C) 2011 Elsevier Ltd. All rights reserved.