The (p, rho, T, x) properties for binary mixtures of CO2 (volume fraction purity 0.99999) and n-butane (mole fraction purity 0.9997) (xi CO2 + x(2) n-butane (x(1)= 0.2322, 0.4794, and 0.7150)) were measured in the compressed liquid phase using a metal-bellows variable volumometer. Measurements were conducted from T = (280 to 440) K and (3 to 200) MPa. The expanded uncertainties (k = 2) were estimated to be: temperature, 3 mK; pressure, 1.5 kPa (p <= 7 MPa), 0.06% (7 MPa < p <= 50 MPa), 0.1% (50 MPa < p <= 150 MPa), 0.2% (p > 150 MPa); density, 0.10%; and composition, 4.4. 10(-4). At > 100 MPa and T = (280 or 440) K, the uncertainties in the density measurements increased to 0.14% and 0.22%, respectively. The data were compared with the available equation of state. The excess molar volumes, v(m)(E) of the mixtures were calculated and plotted as a function of temperature and pressure. (C) 2010 Elsevier Ltd. All rights reserved.