The densities and speeds of sound of (cyclohexane + nonane) were measured at four temperatures from 298.15 K to 328.15 K, and the respective values of excess volumes V-m(E) and adiabatic compressibility were calculated. Thereafter, the densities for the last system were measured at elevated pressures (0. 1 to 40) MPa at four temperatures over the range 298.15 K to 328.15 K with a high-pressure apparatus. The high-pressure density data were fitted to the Tait equation and the isothermal compressibilities were calculated with a novel procedure with the aid of this equation. The low- and high-pressure values of V-m(E) calculated from the density data show that the deviations from ideal behaviour in the system decrease slightly as the temperature and pressure are raised. The V-m(E) data were fitted to the fourth- order Redlich-Kister equation, with the maximum likelihood principle being applied for the determination of the adjustable parameters. (C) 2007 Elsevier Ltd. All rights reserved.