Abstract: A method is disclosed for measuring the concentration of a low molecular weight alcohol, such as methanol, in an aqueous solution. The method uses a fuel cell sensor that includes an anode chamber for electrochemical oxidation of the methanol, a cathode chamber for electrochemical reduction of oxygen; a proton conducting membrane arranged between the anode and cathode; and a voltmeter operatively connected to the anode and cathode chambers. An aqueous solution of the methanol is fed to the anode chamber while the fuel cell sensor is operated at an open circuit state, thereby allowing the methanol to crossover to the cathode where it is oxidized. The open circuit voltage across the anode and the cathode is measured using the voltmeter and the concentration of the methanol is determined from the open circuit voltage.