AbstractSolutions of linearized Navier‐Stokes equations have been developed for the motion of arbitrary two‐dimensional waves occurring at any interface between the emulsion phase of a fluidized bed and the particle‐free, fluid phase. In all cases for which the bed particles are denser than the fluidizing fluid the solutions showed that the lower interface of a bed always is unstable and the upper, stable. The quality of fluidization is suggested to be related at least in part to the rate of growth of surface waves, this rate depending upon physical properties of the system and length of the disturbing wave.