Abstract: A method of removing gaseous inclusions from a highly viscous liquid (10) that comprises applying sonic energy, as by means of acoustic horns (11), or other suitable acoustic source, in the liquid (10) at an energy intensity sufficient to induce migration and coalescence of the inclusions in the liquid (10), and less than that required to produce substantial cavitation therein, until the volume density of the inclusions has been reduced to a desired level. Typically the frequency and the energy intensity are selected, and adjusted if necessary, to provide a mode of operation whereby the liquid (10) is subjected to a cyclic component of stress that causes bubbles to collide and form larger bubbles, and to a substantially unidirectional component of stress, due to viscous losses and other mechanisms occuring in an acoustic field (e.g.