Densities were determined experimentally over the entire range of composition at 298.15 K for the ternary system acetonitrile (1) + acetophenone (2) + 1,2-pentanediol (3) and for the three corresponding binary systems. Excess molar volumes were calculated for the binary and the ternary systems. These results were fitted to variable-degree polynomials. Further, the Prigogine-Flory-Patterson (PFP) theory and Extended Real Associated Solution (ERAS) model were applied to V E m for the binary mixtures of acetonitrile + acetophenone, acetonitrile + 1,2-pentanediol and acetophenone + 1,2-pentanediol, and the findings compared with the experimental results