Isentropic compressibilities kappa(S), and excess isentropic compressibilities kappa(S)(E) have been determined from measurements of speeds of sound u and densities rho of 14 binary mixtures of triethylamine (TEA) and tri-n-butylamine (TBA) with n-hexane, n-octane, iso-octane, n-propylamine, n-butylamine, n-hexylamine and n-octylamine. The relative magnitude and sign Of K E have been interpreted in terms of molecular interactions and interstitial accommodation. The values of kappa(S)(E) for TEA + alkane are positive while for TBA + alkane are negative. The values of kappa(S)(E) for TEA + primary amine become progressively less positive and eventually to negative with the increase in chain length of alkylamine. In case of TBA + primary amine, the values of K E increase from n-propylamine to n-butylamine, and then decrease with chain length of primary amine. The experimental speeds of sound u have been analyzed in terms of collision factor theory, free length theory and Prigogine-Flory-Patterson statistical theory of solutions. (C) 2003 Elsevier B.V. All rights reserved.