The binary vapor-liquid and liquid-liquid equilibria and molar excess enthalpies of alkanoic acid mixtures are correlated well using a new associated-solution model whose equilibrium constants are defined in terms of the volume fractions of chemical species and using association parameters for dimerization of acid molecules calculated from the vapor pressures of the pure acids. The model shows a good performance in predicting ternary vapor-liquid equilibria of the acetic acid + toluene + n-heptane system, ternary liquid-liquid equilibria of alkanoic acid mixtures including water and a non-associated component, and ternary excess molar enthalpies of the acetic acid f methanol f tetrachloromethane system from only binary parameters.