Oxidation of bulk samples of (Al) by water and H2O/CO2 mixture at sub-and supercritical conditions for uniform temperature increase and at the injection of H2O (665 K, 23.1 MPa) and H2O/CO2 (723 K. 38.0 MPa) fluids into the reactor has been studied. Transition of (Al) into AlOOH and Al2O3 nanoparticles has been found out. Aluminum samples oxidized by H2O and H2O/CO2 fluids at the injection mostly consist of large particles (300-500 nm) of alpha-Al2O3. Those oxidized for uniform temperature increase contain smaller particles (20-70 nm) of gamma-Al2O3 as well. Mechanism of this phenomenon is explained by orientation of oxygen in H2O polar molecules to the metal in the electric field of contact voltage at Al/AlOOH and Al/Al2O3 boundary. Addition of CO2 to water resulted in CO, CH4, CH3OH and condensed carbon, increase in size of Al/Al2O3 nanoparticles and significant decrease in time delay. In pure CO2 (Al) oxidation resulted in oxide film. Using temperature and time dependences of gaseous reactant pressure and Redlich-Kwong state equation, kinetics of H-2 formation has been described and oxidation regularities determined. At aluminum oxidation by H2O and H2O/CO2 fluids, self-heating of the samples followed by oxidation rate increase has been registered. The samples of oxidized aluminum have been studied with a transmission electronic microscope, a thermal analyzer and a device for specific surface measurement. The effect of oxidation conditions on the characteristics of synthesized nanoparticles has been found out. (C) 2010 Elsevier B.V. All rights reserved.