Apparatus for removing carbon dioxide from a stream of air or other gas, which includes a vertical gas absorption reactor containing loosely packed mixing units submerged in a carbon dioxide absorbent liquid; gas to be treated is admitted at or near this base of the rector, is broken into small bubbles by the mixing units, and passes through the absorbent liquid to remove a high percentage of carbon dioxide; treated gas leaves from the top of the reactor, a regenerator associated with the reactor continually or intermittently regenerates the absorbent liquid and is arranged to receive absorbent liquid to be treated through an outlet from the reactor which is located higher up the wall of the reactor than the inlet for returning treated liquid to the reactor.