A theoretical study to predict spout-annulus, interfaced variation with bed level for different column geometries of spouted beds is proposed; A previous mathematical model (Krzywanski, et al., 1989), developed for spout shape predictions in two-dimensional spouted beds, is here proposed to be. applied also for cylindrical, conical or cone-based 1 cylindrical columns. Its predictions depend on the, average spout diameter and on the spout expansion angle. While there exists empirical equations available to estimate the first model parameter, the second requires a rigorous stress analysis of the particles at the, entrance of the bed. To avoid this difficulty, this work proposes a simple mathematical strategy to calculate the spout expansion angle. The reliability, of this',, approach was checked by comparison with several experimental results obtained in cone-based cylindrical (Lim et al., 1974; Wu et al., 1987; He et al., 1998) and: rectangular (Zanoelo, 1994) spouted beds.