Abstract: An apparatus is disclosed for rapidly and efficiently dissolving gases in a liquid. A diffuser, having a closed top and an opened bottom, preferably in the form of a conical-shaped frustum having a plurality of openings around the perimeter near the closed top, is submerged in the liquid and rotated at relatively high speeds creating a centrifuge-pump. When the rotating diffuser is located near the surface of the liquid, no additional gas is required in the dissolution process because gas from the surface of the liquid is introduced by cavitation. When the device is submerged substantially below the surface or if a gas other than oxygen is to be dissolved, additional gas must be pumped into the bottom opening of the rotating diffuser or very near the high velocity horizontal liquid jets on the periphery of the diffuser. This device can be used in the oxygenation of treated sewage water, the removal of impurities from liquids, and the oxygenation of horticultural ponds to increase production.