The densities, viscosities and speeds of sound for the binary mixtures of N-methyl-2-pyrrolidone (NMP) with aniline (AB), bromobenzene (BB), and chlorobenzene (CB), over the entire composition range have been measured at T = (308.15, 318.15) K and atmospheric pressure. From these experimental values, excess free volume, excess internal pressure and deviations in acoustic impedance are computed and fitted to a Redlich–Kister type polynomial. The results are interpreted in terms of molecular interactions between the component molecules. Thermodynamic parameters under study suggest the existence of strong interactions between NMP and AB, or BB, or CB.