Densities and ultrasound speeds of benzyltrialkylammonium chlorides (BTAACls) were measured accurately in aqueous solutions at five temperatures (293.15, 303.15, 313.15, 323.15, and 333.15) K. The data were utilized in determining apparent molar volumes, V-phi, and apparent molar isentropic compressibilities, K-S phi. Infinite dilution values of these apparent molar quantities, V degrees(phi) and K degrees(S phi), were determined by extrapolation procedures. Contribution of CH2 groups, along the alkyl groups of BTAACls, to V degrees(phi) and K degrees(S phi) values were derived from plots of these quantities as a function of number of additional CH2 groups in going from benzyltrimethylammonium chloride to benzyltributylammonium chloride. The temperature dependencies of V degrees(phi) and K degrees(S phi) values were examined on the basis of isobaric expansivity. Apparent molar isobaric expansivities at infinite dilution, E degrees(phi), were obtained from the slopes of V degrees(phi) versus temperature data. Concentration dependencies of V-phi and K-S phi were examined. A fair correlation was observed between V degrees(phi) and K degrees(S phi) values of the three BTAACls. (C) 2009 Elsevier Ltd. All rights reserved.