Abstract: Non-uniform distribution of valve tray entrainments on the tray efficiency has been systematically investigated. This effect arises from the existence of concentration differences along the liquid flow path on the tray. A model is given for the prediction of apparent tray efficiency for various forms of entrainment distribution along the liquid flow path on the tray. It is reasonable to have the non-uniformity of distribution of entrainment expressed as the relative ratio of the first order moments of both halves of the entrainment distribution function about the center line of the tray. In general, with more entrainment distributed at the liquid outlet region of the tray, the apparent tray efficiency is reduced and this effect is enhanced by increases in Peclet number, stripping factor, entrainment fraction and point efficiency. Apparent tray efficiency predicted on the assumption of uniform distribution of entrainment is either under-estimated (approximately up to 5% with entrainment predominating at the inlet tray area), or over-estimated (up to 8% with entrainment predominating at the outlet tray area). The moment data of the valve tray is given by empirical correlation based on experimental work done by the authors. Experiments are carried out over a wide range of tray conditions.