Measurements on bubble rise velocity in the region where transition from the bubbling regime to the slugging regime occurs are reported. Observations were made in two beds of internal diameters equal to 22.4 and 61 cm. Bubbles were injected near the bottom of incipiently fluidized beds, and the technique of change in capacitance was employed to probe bubble rise velocity. Glass beads of three different size ranges were used as the fluidizing particles; their surface mean diameters were 59, 68, and 198 μm. Employing the present data (combined with some published data) a simple equation of bubble rise velocity applicable to the full range of flow regimes in fluidized beds was formulated. Such an equation is useful in developing computer models simulating the behavior of both bubbling and slugging beds. A comparison of the simple equation with those reported in the literature for gas-liquid systems is also presented.