Four samples of carbon black were synthesised for use in aqueous supercapacitors. They were designed to have different surface areas and pore size distributions. The objectives were to identify the attributes that are necessary to obtain a high specific capacitance and to attempt to correlate different physical characteristics of the carbon electrodes with their capacitance. A fifth carbon was obtained from another laboratory for comparison. Carbon electrodes were analysed using both acidic and alkaline electrolytes. Their capacitance was measured at room temperature and at −40°C, using slow sweep cyclic voltammetry. Electrochemical impedance spectroscopy was also performed on the carbon electrodes using the same electrolytes and temperatures. The results from these measurements are discussed in terms of the surface areas and pore size distributions of the samples, which were measured using the BET technique.