Densities, rho, ultrasonic speeds, u, and viscosities, eta of binary mixtures of toluene with acetonitrile (AN), propionitrile (PN) and butyronitrile (BN), including those of pure liquids are measured over the entire composition range at temperatures 298.15, 303.15 and 308.15 K, respectively. From these experimental data, excess intermolecular free length, L-f(E), the deviations in ultrasonic speed, Delta u, excess acoustic impedance. Z(E) and excess free energy of activation Delta G*(E) are calculated. The variation of these excess parameters indicates the presence of specific interactions between toluene and AN/PN/BN molecules, and the interactions follow the order: AN > PN > BN, i.e., the toluene-nitrile interaction decreases with increase in alkyl chain length. Moreover, the theoretical ultrasonic speeds are computed based on the scaled particle theory and compared with the experimentally measured values. (C) 2009 Elsevier B.V. All rights reserved.