The effect of the geometric factors of the contactor and of the operating conditions on the geometry of the spout and fountain has been studied by means of an optical fiber probe. In the fountain, the core or solid ascending zone and the periphery or solid descending zone have been delimited. The materials studied are glass beads and different plastics (polyethylene, polypropylene, and polystyrene, both extruded and expanded). A correlation proposed for the calculation of the average spout diameter in cylindrical spouted beds of a conical base has been proven to be valid for these materials of low density. New correlations are proposed for the calculation of the height and width of the fountain.