A reliable method was developed to study bubble behavior by analysis of vibration signals in fluidized beds. The advantage of this method is that the vibration probe is in indirect contact with the process. Accelerometers were used to record vibration signals generated by particle flow through the fluidized bed at various superficial gas velocities and particle sizes. Measurement of vibration signals, sampled at 25 kHz for 30 s, enabled investigation of changes in flow structure related to flow regime transitions. To study bubble behavior under different conditions, different particle sizes were used in the experiments. The measurements were extensively analyzed using wavelet and fast Fourier transforms. Results indicate that the vibration frequency generated by bubbles is between 1000 and 3000 Hz. The vibration analysis was effectively used to detect minimum fluidization and transition from bubbling to slugging in gas-solid fluidized beds. (C) 2009 Elsevier B.V. All rights reserved.