Solids and gas efflux rates have been measured for multiple circular and slot openings on the inner boundary of an annular fluidized bed. Square-edged and sharp-edged orifices were used with copper concentrate particles of mean diameter 64, 90 and 159 μm. Solids efflux results are in good agreement with those obtained by previous workers using single orifices and more rounded particles. Temporal and spatial uniformity of the solids efflux are satisfactory. Gas efflux rates were found to exceed theoretical estimates. The annular fluidized bed feeder appears to offer attractive advantages of high solids—gas loading ratios, uniform flow, good controllability and simultaneous reactor wall cooling and feed stream preheating for high-temperature short residence time reactors.