Abstract: An apparatus and method for introducing gas into a liquid is disclosed. The apparatus comprises: a conduit (20); a fluid directing formation (10) arranged within said conduit and defining a plurality of discrete channels within said conduit, said channels being isolated from each other in a direction perpendicular to a direction of fluid flow through said channels, each channel providing a flow accelerating constriction to said fluid flow such that fluid flowing in each of said channels is caused to accelerate as it flows through said flow accelerating constrictions; wherein at least some of said channels comprise orifices within said flow accelerating constrictions, said orifices being in fluid communication with a gas source, such that said gas is drawn through said orifices to be entrained in said fluid flow by virtue of a reduced pressure in said channels caused by said fluid flow.