The present invention concerns a method and equipment for dissolving a gas or a gas mixture in a liquid. The liquid is introduced into a chamber (6) via an inlet (2), in connection with which an eddy movement is created in the chamber for mixing the gas and liquid. The gas may be introduced into the liquid before the liquid is introduced into the chamber and/or the gas may be introduced directly into the chamber. The liquid with the dissolved gas is removed via an outlet (4). The gas is dissolved in the liquid by the eddy rotating about a mainly horizontal axis. With the present invention, satisfactory dissolution can be achieved with minimal energy consumption. The present invention is particularly well suited to oxygenating salt water, for example in connection with fish farming.