Two adjacent fluidized beds separated by a wall can exchange solids through an orifice due to the local pressure oscillations on both sides of the orifice produced by passing bubbles. This flow of solids between the two fluidized bed reactors is sufficient for some practical applications where a highly integrated, simple and cost-effective arrangement might be required. Solid transfer rates through orifices of different geometries and dimensions have been measured in this work using a novel image analysis technique. The measured solid fluxes can reach up to 60 kg/m(2)s in some experimental conditions. An empirical correlation has been proposed to fit the available experimental data as a function of key operating conditions. (C) 2004 Elsevier Ltd. All rights reserved.