Flow behavior of three-phase flow was studied using a two-dimensional draft-tube fluidized bed operating with air, water and alginate particles (d(s) = 2.5 mm, rho(s) = 1040 kg/m(3)). Momentum transfer between a particle and three-phase flow was assessed from settling velocities of tracer particles with diameters of 2.5 and 5 mm, and densities 1100-2500 kg/m(3). The settling velocities of tracer particles were systematically lower than the corresponding free-settling velocities, as a result of additional momentum transfer with air bubbles and fluidized bed particles. These effects were separated by comparative studies of particle settling in two-phase and three-phase how. Mechanics of particle motion in three-phase flow was modeled in terms of the effective particle buoyancy and the effective drag coefficients.