A comprehensive composite database for distillation sieve-tray efficiency is used to develop point efficiency and entrainment correlations based on a model that considers the fluid on the distillation tray to be contained in a liquid-continuous region near the fray deck and a vapor-continuous region on top of the liquid-continuous region. This model allows estimates of the portion of the mass transfer that occurs in each region and the mass-transfer resistance that occurs on the liquid side and vapor side of the interface. For most cases, most of the mass transfer occurs within the liquid-continuous region. The liquid side resistance is often significant. The entrainment correlation is consistent with the work of Bennett et al., which relates entrainment to the ratios of the liquid to vapor density and the froth height to the tray spacing. A simple liquid continuous-only mass-transfer model containing only four empirical parameters correlates the point efficiency data to within 6.4%. Despite a twofold change in vapor Schmidt number, no dependency on vapor Schmidt number is seen. Important dimensionless groupings are the Reynolds number based on the hole velocity, effective froth density, ratio of tile liquid inventory to the perforation diameter and fraction of the tray area perforated Mathematically simple and accurate methods allow the prediction of the section efficiency for trays operating in cross ol par allel flow They address vapor and liquid miring, entrainment and a criterion to avoid significant degradation of the tray efficiency due to weeping.