p rho Tx-property measurements near saturation in the gaseous phase for propane (1) + isobutane (2) at x(1) = 0.25 (w(1) = 20.19 %), x(1) = 0.5 (w(1) = 43.14 %), and x(1) = 0.80 (w(1) = 75 22 %) are reported. The data near saturation in the gaseous phase are important information for deriving reliable property values such as specific heats near saturation or for determining the second and third virial coefficients. The measurements were performed using a magnetic Suspension densimeter. 154 p rho Tx values for propane + isobutane mixtures were obtained at the temperatures of(303.15 and 323.15) K and for pressures up to 980 kPa. The experimental uncertainties are estimated to be 10 mK for temperature, 0.45 kPa for pressure, (0 03 % + 0.005 kg.m(-3)) for density, and 0 31 % in mass fraction (0.32 % in mole fraction). The purities of propane and isobutane were both 99.99 % in mass fraction according to the report From the manufacturer The measurements are used for assessing the reliability of existing equations of state.