The working mechanism of a ceria-supported Cu (Cu-at:Ce-at = 1:10) system in the Catalytic Wet Oxidation (CWO) of phenol with O-2 (T-R, 130-170 degrees C; P-O2, 7 atm) has been thoroughly assessed. Basic relationships amongst pH, extent of leaching and rate of phenol and TOC conversion prove the major contribution of a homogeneous catalytic path by Cu ions on the peculiar CWO pattern of supported copper catalyst. In addition, gas-phase reduction/oxidation tests signal the lack of reversibility of the redox cycle of the CuCeOx system under typical reaction conditions.