This communication examines experimental information from the literature on the volume contraction that can occur when two monocomponent particle species that have a diameter ratio and a buoyancy-corrected density ratio on opposite sides of unity are subjected to liquid fluidization as a binary mixture. Attempts are made to predict this volume contraction by applying monocomponent bed expansion equations using averaged properties of the binary solids. It was found that this method works better if the equations are anchored to experimental monocomponent voidages by the fractional bed volume change that they predict than if the equations are used directly. However, greater prediction accuracy can be achieved by correlation of the adjustable parameter G of the Westman, Am Ceramic Soc, 19, 127 - 129, (1936) equation, originally applied to binary packed beds.