Oxidations of C2H4 and C3H6 were performed using an [alkene\Pd black (anode)\H3PO4\graphite (cathode)\NO+O-2] gas cell at 353 K. The cofeed of NO with O-2 at the cathode dramatically enhanced the Wacker-type oxidations of the alkenes. The enhancement was ascribed to the acceleration in the rate of electrochemical oxidation of Pd(0) to Pd(II) due to the formation of NO2 at the cathode. The formation of NO2 increased the electromotive force of the cell and the polarization at the Pd anode. The graphite without precious metals was sufficient as the cathode for the reduction of NO2 into NO under the reaction conditions in this work. The NO cofed with O-2 works as a mediator for the electrochemical reduction of O-2 In the case of propene oxidation, acetone was the major product for the C3H6-(NO+O-2) cell. The formation of acrolein, the major product for the C3H6-O-2 cell, was decreased markedly when NO had been cofed with O-2. These observations could be ascribed to the changes in the concentrations of Pd(0) and Pd(II) responsible for the pi -allyl and Wacker type oxidations, respectively. (C) 2001 The Electrochemical Society. All right reserved.