An apparatus, designed to simulate bubbling of a sieve tray operated in froth regime, was employed.Bubble contact angles in and above the incipient weeping regime for an air-water-plexiglas system were investigated.The influence of both liquid cross-flow and gas up-flow upon bubble contact angles was examined. A model considering the influence of liquid cross-flow was developed to predict bubble size from a sieve hole in froth operation regime.The comparison shows that the bubble sizes predicted by the present model are consistent with our experimental values and the available published experimental data.