The paper addresses phenomena associated with the hydrodynamic interaction between a gas-emitting coarse particle and a gas-fluidized bed of finer solids. The study is relevant to segregation of particles undergoing fast decomposition (e.g. solid fuel pyrolysis) in fluidized beds.Hydrodynamic patterns associated with gas-emission from a coarse particle into a gas-fluidized bed have been characterized by means of 2D experiments by simulating the gas-emitting particle as a porous cylinder. Formation of endogenous bubbles around the gas source was highlighted.The momentum exchange between bed solids and the gas-emitting particle was characterized by means of experiments carried out in a cylindrical fluidized bed. The gas-emitting particle was simulated by a porous sphere connected to a gas source and continuously weighed. Gas-emission from the sphere induced momentum transfer from the fluidized suspension to the sphere resulting into a lift force opposed to gravity.Quantitative assessment of the lift force was based on analysis of data obtained with different gas-emitting sphere sizes, gas superficial velocities and flow rates of emitted gas. (C) 2003 Elsevier Science B.V. All rights reserved.