In this work, the effect of gas velocity on the electrostatic charge generation in gas-solid fluidized beds was studied with a specific focus on the transition to turbulent flow regime. Experiments were conducted at a pressure of 2600 kPa (abs) with fluidizing gas velocities of 1.5, 3, and 5 times of U-mf (pre-turbulent regimes) and 7.5 times of U-mf (turbulent regime). Increasing the gas velocity and transitioning to the turbulent flow regime improved particle-wall contacts; and thus, augmented the extent of wall fouling, which indicates the increase in bed electrostatic charge generation. The amount of fouling was approximately five times larger in turbulent flow regime (7.5 U-mf) in comparison to that for the lowest gas velocity examined in bubbling flow regime (1.5 U-mf). The particles coating on the column wall consisted of a thick bottom layer which extended to a height of approximately 1 m above the distributor plate, and a thin top layer which extended to the top of the column near the outlet. The particles net specific charge in the top and bottom layers did not vary with the increase in gas velocity. However, the net charge of these particles increased. The fine particles entrained from the bed had a net negative charge resulting in a net positive charge to be left behind in the bed contributing to the increase in the magnitude of wall fouling at higher gas velocities, especially in turbulent flow regime. (C) 2017 Elsevier B.V. All rights reserved.