A new group-contribution method to obtain the PC-SAFT molecular parameters of nonassociated compounds (linear alkalies, branched alkanes, linear monoethers, and esters) is developed on the basis of their regular trends against molecular mass. The method takes into account the proximity effect among all functional groups of a molecule in order to describe the deviations of shorter chain molecular parameters from the regular trend observed for the larger chain ones. The group-contribution scheme considers the molecular parameters as a linear combination of reference functional-group parameters and their mutual perturbations, which are responsible for the deviations from the reference ones. Both types of parameters (the reference functional-group parameters and the mutual perturbations) are optimized to the available molecular parameters published in the literature and obtained by direct fitting from experimental data of saturation pressures and saturated liquid densities.