The characteristics of solids global fluctuation in gas fluidized beds was examined. It was identified that sloshing is a dominant mechanism in bubbling fluidized beds. Experiments were conducted using the computer-aided particle tracking facility to examine the solids sloshing motions and to determine the fluctuation frequency. For cylindrical beds of intermediate depths, there are two modes of sloshing; namely, the axisymmetric mode and the antisymmetric mode. A standing surface wave model has been developed to predict the global fluctuation frequency of the solids sloshings in beds of intermediate and shallow depth. The axisymmetric and the antisymmetric modes of sloshing in cylindrical beds are the full- and half-wave modes of the standing surface waves. The model predictions for the sloshing frequency were found to be in good agreement with the experimental data of this study and with others in the literature. More importantly, it was found that, although the excitation for bed fluctuations originates from bubbles, the fluctuation frequency is controlled by surface waves.