The segregation of fuel particles in a fluidized bed combustor or gasifier is of primary concern for efficient operation of reactors. In this study, the interaction between a single, low density, large sphere and a bubbling bed of glass beads has been investigated via 3D computer simulations. It is shown that the low density sphere which was put on the bed's free surface was pushed into the bed by convective currents. The predicted self-segregation of the low density sphere in a bubbling bed by the model is validated with experiments. (C) 2011 Elsevier B.V. All rights reserved.