Opportunities given by applying the PC-SAFT (Perturbed Chain-Statistical Association Fluid Theory) for estimating and calculating the speed of sound in natural gas were considered. Examples are presented of prognosticating the density and the speed of sound for five multicomponent gas mixtures containing alkanes, isoalkanes, nitrogen, and carbon dioxide in a wide range of temperatures and pressures (250–450 K and 0.5–60 MPa). The results of calculations are compared with published experimental data. It is shown that the model reproduces with high precision the experimental values of the density and the speed of sound.