The stability of an assembly of particles which are suspended in a flow field of a gas, under the action of force fields, is considered. It is shown that the stability of the particle dispersion depends on the composite energy density due to the flow and the force fields. The stability can be maintained by balancing the change occurring in the flow and force fields, so that the total energy density after the change remains fixed. This capability is well established in Magnetically Stabilized Fluidized Beds (MSFBs), where the magnetic field can be used to lower the energy of the system against the rise in die kinetic energy of the fluidizing gas. A general criterion for stability is formulated in terms of the balance between energy densities that can be assigned to the dispersion as a composite entity. The sedimentation behavior of particles fluidized by gas discloses the factors that affect the intensity of instability of these systems. Simulation of batch sedimentation of concentrated, i.e. low voltage, polydisperse particle mixtures shows that the evolution of voltage disturbances is enhanced at higher particle concentrations and narrower size distributions. Under these conditions, relaxation time of the system becomes too high so that the evolution of the disturbance cannot be suppressed. This behaviour is the result of fluid particle interaction and the high sensitivity of the system to relatively small voltage perturbation. The application of polarization fields can eliminate this high sensitivity and render the system more stable. The extra stability is achieved by formation of ordered, pearl chain structures of the polarized particles. These structures render the system higher permeability levels to the flow of gas, thus allowing higher velocities at the same pressure drop. Alternatively, the formation of pearl chains changes the fluid particles interactions, decreasing the fluid drag and increasing the sedimentation velocity of the particles.