In this work, speeds of sound for ternary and quaternary mixtures composed of tetralin, decalin, n-decane, and n-hexadecane were experimentally determined at pressures of 0.1, 5, 10, 15, 20, and 25 MPa and temperatures of 313.15, 323.15, and 333.15 K. Additional density data at atmospheric pressure for the same systems were measured experimentally at temperatures of 313.15, 323.15, and 333.15 K. From these results and thermodynamic definitions, densities at high pressures were calculated. The experimental data were correlated with the PC-SAFT equation of state. For pure components and mixtures the PC-SAFT model failed to reproduce the density dependency with temperature, correlating this property with deviations higher than the experimental uncertainty. For speed of sound the model failed to reproduce this property dependency with temperature and pressure. To improve SAFT-like equations of state performance for modeling speed of sound, a better description of the repulsive interactions in the model is needed.