A thorough understanding of the hydrodynamics in tray columns is required to optimise column and tray design for specific operating capacities and conditions. Liquid transported by the rising gas to the tray above, defined as entrainment, is one way of measuring the tray column capacity limit. Entrainment correlations available in the literature have been developed with predominantly air/water data, because of the limited availability of non-air/water data. In this work an experimental setup was constructed to measure entrainment, tray pressure drop and weeping for various gas and liquid systems. The experimental entrainment data for three systems, namely air/water, air/ethylene glycol and air/silicone oil, is compared to existing correlations. The effect of liquid physical properties on entrainment under flow factors ranging from 1.6 kg(0.5)/(m(0.5) s), for a 415 mm tray spacing to 4.0 kg(0.5)/(M-0.5 s) for a 615 mm tray spacing within a liquid flow range of 2.9-112 m(3)/(h m) was observed. The experimental results showed a somewhat complex dependency of entrainment on liquid physical properties. At gas flow factors of 2.2 kg(0.5)/(m(0.5) s) for the 415 mm tray spacing, entrainment reached a maximum in the froth regime and then decreased with increasing liquid rates. Notably, the liquid viscosity - not included in previously developed correlations - significantly influences the entrainment behaviour. Existing entrainment correlations agree better with the air/water data than with the air/ethylene glycol or air/silicone oil data. (C) 2012 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers.