A simple model for the description of flow behavior in three phase (solid-liquid-gas) airlift reactors (TPAL) was developed. Based on an energy balance, which takes into account the dissipation of energy in the phase interfaces, the model predicts liquid and solid circulation velocities, gas holdup and solid distribution within the reactor. It describes the three flow modes in relation to the solid behavior as the gas flow increases, namely, packed, fluidized and circulating beds and establishes the boundary conditions between the flow modes with accuracy. The hysteresis effect widely described in literature is also predicted, the initial solid holdup distribution (epsilon(s)(00)) is the main parameter to describe this effect. Experimental data obtained by various authors for reactors of different shape (internal or external loops) and size (from 0.020 to 284 m(3)), different solid particles (sizes from 0.1 to 3 mm and solid densities from 2550 to 3700 kg/m(3)) and different experimental conditions are simulated satisfactorily.