The influence of gas velocity (3.5, 10, and 18 mm/s), salt type (NaCl, NaF, NaBr, Nal and CsCl) and salt concentration (0.001-3M) on bubble coalescence in a small bubble column were studied. The bubble coalescence was determined by the relative change in the measured light intensities passing through the salt solutions and clean deionised water. It was shown that the transition salt concentration for bubble coalescence inhibition (determined at 50% of bubble coalescence) of all investigated salts decreases with increasing superficial gas velocity. The difference in the transition concentration between NaCl, NaF, NaBr and CsCl does not significantly change with the gas velocity. However that difference between Nal and the other salts significantly decreases with increasing the gas velocity. The gas holdup significantly increases with NaCl, NaF, NaBr and CsCl concentrations but does not significantly change with NaI concentration. These new results imply that the transition salt concentration for bubble coalescence and gas holdup depend not only on the salt properties (i.e. the ion type and their combination) as previously reported, but also on the hydrodynamic conditions. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.