A twin flow type of mixing calorimeter was constructed for measuring excess enthalpies of fluid mixtures over wide temperature and pressure ranges. The precision of the calorimeter was tested with (water + ethanol) mixture. The excess molar enthalpies H-m(E) for the (water + ethanol) mixture at temperatures T = (423.2 and 523.2) K and pressure p = 5.00 MPa and at T = 523.2 K and p = 15.00 MPa are in good agreement with the literature values. The H-m(E) values for the (benzene + cyclohexane) mixture were measured using this calorimeter over the temperature range from T = 298.2 K to T = 573.2 K and the pressure range from p = 5.00 MPa to p = 25.00 MPa. All H-m(E) values are positive and all mole fraction dependencies of H-m(E) are almost symmetrically parabolic. The maximum values of the mole fraction dependence of H-m(E) decrease with increasing temperature and are independent of the pressure, except for the conditions at T = (498.2 and 523.2) K and p = 5.00 MPa whose states are near the critical point of benzene. The maximum values of H-m(E) of these states were greater than the values expected from the curve representing the temperature dependence of other maximum values of the mole fraction dependence of H-m(E). (C) 2014 Elsevier Ltd. All rights reserved.