The effect of compactness and pressure on the conductivity of supercapacitor electrodes and their resulting electrochemical properties is studied. Mixtures of cobalt oxides MxCoO2 (M = H or Na) with carbon and polymer additives are studied under pressures up to 20 MPa. A power function links the compactness and the resistivity of the powder formulations in this pressure range, coherent with powder rearrangement and grain packing. Although the cobalt oxide grains have a metallic character, the powders remain quite resistive because of weak connections between the grains. Carbon additives enhance the intergranular conductivity in dry formulations and the resistivity mainly depends on the carbon volume content. Electrochemical measurements on a symmetric cell using formulated electrodes in a Na2SO4 electrolyte clearly show a large positive effect of the pressure on the electrochemical performances of the cell: After release of the pressure, the electrode retains a part of its optimum performance.