This paper examines the fundamental characteristics of an inverse gas-liquid-solid turbulent bed. In this reactor, solids lighter than water, of large diameter (3-4 mm) and of densities ranging from 914 to 934 kg/m(3), are fluidized by only an upward gas flow. The hydrodynamic behaviour is described and characterized by some specific gas velocities. Particles are easily fluidized and can be uniformly distributed over the whole height of the column. The effect of the operating conditions (column diameter, gas sparger, initial weight of particles introduced into the reactor) on the hydrodynamics is presented. A simplified model is proposed to predict the values of one of these gas velocities.