The effect of distributor type and geometry on the expansion of particles has been studied in a fluidized bed of 300 mm diameter and 800 mm deep. Four distributors were examined; three perforated plates, each perforated by holes of 0.8 mm in diameter but different hole densities at 6 mm, 9 mm and 12 mm pitch, and a porous plastic Vyon distributor 17 mm thick were examined. Particles of different materials in sizes were fluidized, 37 tubular inserts were held vertically as arrays in the bed. All experimental data for four distributors were correlated within experimental error by the equation: (U-U-mf/U-0-U-mf)=(e-e(mf)/1-e(mf))((1.28+0.00033P3)) with sigma (2)=0.028996 Where U, U-mf, U-0 are the gas velocity, velocity at minimum fluidization and real or apparent terminal velocity, while e is the bed porosity and e(mf) is the porosity at the condition of minimum fluidization. P is the hole pitch of perforated plate distributor in millimeters.