The automatic degassing valve allows for continuous venting of undissolved gas from the contacting vessel of an ozone treatment system. Placed at the high point of a piping system, the degassing valve vents gas as it occurs. A unique float, or actuating lever, allows the vent to open when gas is present. After the gas vents out, the liquid forces the vent to close. Whenever gas accumulates, the valve will re-open until the gas is vented.