Abstract Experiments were conducted in a 0.12-m-in-diameter bubble column to investigate the effect of electrolytes on gas hold-up ( ε ) and on the regime transition point in bubble columns. Air was used as the dispersed phase and aqueous solutions of three different salts (NaCl, Na 2 SO 4 and NaI), as well as double-distilled water, were utilised as the continuous phase, varying the gas superficial velocity ( u G ) in the range 0–0.26 m/s. The ε × u G curves were a function of both the chemical nature and the concentration of the electrolytes. However, similar ε × u G profiles were obtained regardless of the electrolyte for a given ratio between the concentration in the solution and the critical concentration of the electrolyte for bubble coalescence. This ratio therefore presents itself as a promising modelling parameter to account for the chemical nature of electrolytes. The gas hold-up data were employed to compute the regime transition point according to two different methods, evidencing its non-linear dependence on the concentration of electrolytes in the liquid.