Pneumatic transport of Group C 20 mu m glass beads was studied in a 31.7 mm vertical line, along with 66 mu m Group A glass beads for comparison. Pressure gradients along the riser were measured and the Zenz type state diagrams were constructed for both type of particle. For Group C particles, the results show that the Zenz diagram has the usual characteristic form, but the minimum pressure gradient is much lower and is positioned at a significantly higher gas velocity. Multiple layers of Group C particles were found to adhere to the column wall, while only a fraction of the column inner surface was covered by the 66 mu m particles. The effects of the electrostatics effect during solids conveying was also examined through the addition of anti-static particles and was shown to be less significant for the finer particles. This is because the tube inner surface is entirely covered by the particulates, which reduces the charging since only like materials are then in contact. (C) 2000 Elsevier Science Ltd. All rights reserved.