Abstract: A column reactor, suitable for continuous production of a gaseous reaction product by contacting a liquid reaction medium with a gas-forming agent fixed to a reaction plug comprising a solid substrate provided with a plurality of gas-forming channels. The column reactor overcomes the apparent short circuiting of liquid reaction medium through the reactor by being provided with two or more reaction zones, each zone having its own circulatory by-pass means for liquid reaction medium. To obtain the reaction zones a reaction plug can be divided into two or more spaced apart plug portions. For each reaction zone the circulatory by-pass means provides a portion of the pathway for an internal recirculation current of liquid reaction medium.