Unsteady bubble plume oscillations significantly influence the characteristics of the flow and especially the mixing occurring in bubble column reactors. In the present work, the frequencies of oscillations of centrally aerated bubble plumes in rectangular bubble columns are experimentally studied in water and aqueous glycerol solutions. The effects of the superficial gas velocity, aspect ratio, aerated width, needle size and the liquid viscosity on the low-frequency oscillations are investigated. The performance of the dimensionless numbers characterizing the plume oscillation published in the literature is assessed with the present experimental data. Dimensionless analysis is performed and a new empirical correlation is proposed based on the present experiments, and then validated through a large number of available experimental data in the literature. The experimental data and dimensionless analysis presented here can help to optimize the flow characteristics for specific processes in bubble column reactors. Further, the results can be used for validating corresponding computational models.