Abstract Bed collapse experiments are interpreted by a three-phase model of a gas-fluidized bed. Application of the model leads to a relationship between bed voidage in the sedimentation zone of the collapse and the properties of the emulsion and bubble phases of the bed prior to the collapse. Experimental results show that for beds of small particles fluidized under pressure the flow of gas through the emulsion phase is higher than that expected on the basis of existing theories, but it is shown that average rise velocities of bubbles may be obtained from results of bed collapse measurements.