In order to determine the mechanism of mixing and evaluate its effectiveness in a model mixer, FEM flow profiles generated for a series of purely viscous, shear thinning inelastic and viscoelastic fluids using the techniques previously described in Connelly and Kokini (2003) [31] were used to find trajectories for material points with random initial positions. The mixing mode was shown to be primarily laminar shear using the Manas-Zloczower mixing index [10]. The mixing was analyzed statistically using the segregation scale [5] and cluster distribution index [41], demonstrating its cyclic nature in the model mixer with the type of rheology studied effecting the period of the cycles. Length of stretch and efficiency of mixing was evaluated using the method of Ottino (1989) [18]. They showed some stretching near the walls but overall the efficiency decayed as t(-1), with the effect of the theology evident in the speed of the decay and the negative values in the viscoelastic model results. (C) 2004 Elsevier B.V All rights reserved.