Liquid-liquid equilibria of aqueous solutions of acetic, propionic, butyric, and valeric acids with trioctylamine in various diluents, 1-octanol, chloroform, methyl isobutyl. ketone; and tetrachloromethane, were determined at 298 K. An expression of the extraction equilibrium is derived, and the apparent extraction equilibrium constants (K-11) are evaluated. The predicted loading of trioctylamine agrees well with the experimental values. The relationship between the K-11 and the hydrophobicities of the acids is discussed.