Nonlinear oscillations in continuous fluidized bed spray granulation with external product classification are analyzed. Using methods from numerical bifurcation analysis the size and location of the instability regions in the space of the design parameters and the adjustable operating parameters are predicted and discussed. The analysis is based on a new relatively simple population balance model, which is formulated on a mass basis, and provides first qualitative insights into the nonlinear dynamic behavior of continuous fluidized bed spray granulation processes. (c) 2006 Elsevier B.V. All rights reserved.