Over the past few decades there have been numerous attempts to measure electrostatic charges in gas-solid fluidized bed reactors; these charges have been prone to cause reactor downtime from electrostatic phenomena. In this study, a new system was developed that aimed to quantifying the electrostatic charge generation in three key areas within a gas-solid fluidized bed simultaneously: the bed particles, the particles that adhered to the column wall, and the particles that were entrained from the column. A unique online Faraday cup method was used to measure the electrostatic charge of the particles. The system was operated with dry air at two fluidizing gas velocities, one in the bubbling and the other in the slugging flow regime. An industrial polyethylene resin with a wide particle size range was utilized in all experiments. Results showed the occurrence of bi-polar charging in both flow regimes with entrained fines being mainly positively charged, whereas the bed particles and those attached to the column wall carrying a net negative charge. The charge-to-mass ratio (q/m) of the entrained fines in the bubbling regime was significantly higher than in the slugging regime. It was discovered that particles with a certain size range were predominantly adhering to the column wall with a significantly higher q/m than the other bed particles. These findings led to a proposed mechanism for the migration of particles within the fluidization column due to the effect of electrostatic charge generation. (C) 2010 Elsevier Ltd. All rights reserved.