Characteristics of heat transfer and hydrodynamics have been investigated in two- and three-phase inverse fluidized beds whose diameters are 0.152 and 2.5 m in height. Effects of gas and liquid velocities and particle density (polyethylene and polypropylene) on the immersed heater-to-bed heat-transfer coefficient, individual phase holdup, and minimum liquid fluidization velocity have been determined. It has been found that the minimum liquid fluidization velocity decreases with increasing gas velocity in the inverse fluidized beds. The gas and liquid holdups increase with an increase in the gas or liquid velocity in the beds. The heat-transfer coefficient in two- and three-phase inverse fluidized beds of relatively high density particles (polyethylene) has been higher than that in the beds of relatively low density particles (polypropylene). The heat-transfer coefficient increases with increasing gas velocity; however, it exhibits a maximum value with increasing liquid velocity in liquid-solid as well as three-phase inverse fluidized beds. The liquid velocity at which the h value attains its maximum value decreases with increasing particle density or gas velocity. The immersed heater-to-bed heat-transfer coefficient has been well correlated in terms of dimensionless groups as Nu(1) = 0.001(Pr)(Re-1)(1.282), Nu(2) = 0.084(Pr)(Re-2)(0.944), and Nu(3) = 0.050(Pr)(Re-3)(0.810).