Solids flow direction near the wall of a CFB riser was studied for three monodisperse, two binary mixtures and one continuous particle size distribution (PSD) of Geldart Group B particles. Measurements were taken at five axial positions along a 0.3 m diameter, 18 m tall pilot-scale CFB riser at four operating conditions. The data were compared to predictions available from flow regime maps. Results showed that (i) for monodisperse systems, particle diameter was more dominant in dictating upflow annulus behavior; (ii) the binary mixtures exhibited largely upflow annulus behavior, presumably due to the dominant influence of the larger constituent particles in dictating upflow annulus behavior; (iii) for the continuous particle size distribution (PSD), the impact of this type of polydispersity was more pronounced at lower solid loading conditions; and (iv) the applicability of the available regime maps, which were largely developed based on Geldart Group A particles, was found to be limited for the Geldart Group B and non-monodisperse particle systems investigated in this study. (C) 2016 Elsevier B.V. All rights reserved.