The aim of the present work was to characterize onset of entrainment of one phase into the other based on mean velocity and turbulent kinetic energy at the liquid surface. Experiments were carried out in stirred tanks with different impeller geometries (DT, PBTD, PBTU and D/T = 0.30, 0.45, 0.65) with air-water and xylene-water systems. Mean and r.m.s. velocity profiles near the liquid surface were measured with the help of ultrasonic velocity profiler (UVP). The results are compared with the information available in the published literature. it is observed that the onset of entrainment can be characterized by the turbulent kinetic energy near the free liquid surface. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.