Experiments have been conducted with particles of sand (d(p) = 1,421 mu m), silica sand (d(p) = 171 mu m), glass beads (d(p) = 2,745 mu m) and wax pellets (d(p) = 5,476 mu m) in two- and three-dimensional fluidized beds. In both beds, measurement of pressure drop as a function of superficial air velocity are taken and employed to determine the minimum fluidization velocity and the variation of bed voidage with superficial air velocity. Data analysis has made it possible to understand the nature of frictional forces that the front and back bounding walls of two-dimensional fluidized beds caused on bed particles, as well as their dependence on particle shape. Information useful in the design of fluidized beds has been generated.