The behaviour of a strongly fluidising system composed of iron and glass particles with similar minimum fluidising velocities was studied, under steady and also under unsteady state conditions. The parameters which determine fluidisation behaviour were shown to be the depth of the bottom layer and the fluidising velocity, and, based on these parameters, a correlation was developed for predicting segregation. The downward relative velocity of jetsam particles in the emulsion was measured by two independent methods, and it was also demonstrated that under the conditions of this study only about 1% to 3% of the jetsam particles reaching the layer interface is carried into the upper layer.