Abstract: An electrochemical sensor for sensing a gas dissolved in a liquid. The sensor includes a probe having a cylindrical body and a rounded face. A working electrode, a reference electrode and an auxiliary electrode are buried in the probe body and have distal ends reaching conformingly to the face. A pulsed polarizing voltage is impressed between the auxiliary electrode and the working electrode for polarizing the probe, and a capacitor is provided for storing the charge which flows to the working electrode during periods of polarization. The concentration of the dissolved gas is determined by measuring the voltage across the capacitor.