The phase behavior, density, and constant-volume molar heat capacity (C-p,C-m) of ethane + n-pentane binary mixtures have been measured in the supercritical region and subcritical region at T = 309.45 K. In addition, the isothermal compressibility (kappa(T)) has been calculated using the density data determined. For a mixed fluid with a composition close to the critical composition, C-v,C-m and kappa(T) increase sharply as the pressure approaches the critical point (CP), the dew point (DP), or the bubble point (BP). However, C-v,C-m is not sensitive to pressure in the entire pressure range if the composition of the mixed fluid is far from the critical composition. To tune the properties of the binary mixtures effectively by pressure, both the composition and the pressure should be close to the critical point of the mixture. The intermolecular interactions in the mixture are also discussed on the basis of the experimental results. (C) 2003 Elsevier Ltd. All rights reserved.