The (p,rho,T,x) properties for {x propane+(1 - x) isobutane} with x=(1.0000, 0.2765, 0.5052, and 0.7468) in the compressed liquid phase were measured by means of a metal-bellows variable volumometer in the temperature range from (280 to 440) K at pressures from (1 to 200) MPa. The mole fraction purities of the propane and isobutane used in the measurements were 0.9999 and 0.9999, respectively. The expanded uncertainties (k=2) in temperature, pressure, density, and composition measurements have been estimated to be less than +/- 3 mK; 1.4 kPa (p <= 7 MPa), 0.06% (7 MPa < p <= 50 MPa), 0.1% (50 MPa < p <= 150 MPa), and 0.2% (p > 150 MPa); 0.09%; and 1.3 center dot 10(-4), respectively. In the region above 100 MPa at T (280 and 440) K, the uncertainty in density measurements increases from 0.09% to 0.13% and 0.22%, respectively. Comparisons of the available equation of state with the present measurements are reported. On the basis of the present results, the excess molar volume V-m(E) of the mixtures was calculated and illustrated as a function of temperature and pressure. (c) 2007 Elsevier Ltd. All rights reserved.