It is shown that the liquid–liquid interfacial tension in binary and ternary aqueous–hydrocarbon systems at any temperature can be determined by knowing the molar compositions of the bulk fluid phases and a system-dependent constant. The system-dependent constant has been found to be related to saturation adsorption. Based on these findings, a new equation has been proposed for reliable prediction of interfacial tension in aqueous–organic systems. The model is simple to use and reasonably describes the interfacial tension of binary water–hydrocarbon mixtures and some ternary aqueous–organic systems. The new equation shows an apparent inconsistency near the critical point which is explained using the underlying mono-molecular layer assumption.