The densities of three mixtures of carbon dioxide and n-heptane and three mixtures of n-butane, n-heptane and n-hexadecane were measured. The binary mixtures were studied over the temperature range of 302-459 K and the pressure range of 3.61-55.48 MPa at the following carbon dioxide mole fractions: 0.2918, 0.3888 and 0.4270. The ternary mixtures were studied over the temperature range of 405-469 K and the pressure range of 0.7-24 MPa at the following n-butane mole fractions: 0.0904, 0.1564 and 0.1856 and corresponding n-heptane mole fractions: 0.7358, 0.6825 and 0.6588. The measurements were carried out in an automated isochoric instrument and their accuracy is estimated to be better than +/-0.1%. The bubble points of the mixtures were also determined from an analysis of the experimental isochores in the one- and two-phase regions. The new measurements have been used to assess the performance of the Peng-Robinson equation of state and the one-fluid corresponding states model. In single phase regions, the performance of the one-fluid model is found to be superior to that of the Peng-Robinson equation. The latter performs well for bubble points provided that optimised interaction parameters are used. As an interpolation tool, the one fluid model is found to reproduce the ternary mixtures within the experimental uncertainty.