Abstract: An electrochemical gas sensor comprising a sensing electrode, a counter electrode, an electrolyte reservoir, an upwardly extending projection disposed within the reservoir that supports the counter electrode, and a wick interposed between, and in contact with, the sensing and counter electrodes. The wick includes an overhang partially disposed in the electrolyte reservoir. The sensor may further include a reference electrode coplanar with and adjacent to the counter electrode. The sensor is accurate and sensitive, while also compact, reliable, and relatively simple to manufacture.