Cubic Equations of State (EoSs) typically provide unreliable predictions for phase density and derivative properties at the high-temperature, high-pressure (HTHP) conditions associated with ultradeep petroleum reservoirs (that is, temperatures to 533 K and pressures to 241 MPa). The perturbed-chain statistical associating fluid theory (PC-SAFT) EoS returns improved predictions for density but still can overpredict the experimental value by up to 5% at HTHP conditions. Not surprisingly, when a modified set of the pure-component PC-SAFT parameters m, sigma, and epsilon/k are fit to HTHP experimental density data, density predictions throughout the HTHP range agree with reference data to better than +/- 1%. However, the lack of such HTHP density data for many hydrocarbons presents a hurdle to the more widespread use of this PC-SAFT method. This study presents a group-contribution (G-C) method for calculating PC-SAFT parameters that are designed to yield accurate HTHP density predictions. First- and second-order group contributions are considered. We have extended the group contribution model of Tihic and co-workers, developed for polymers, to accurately determine PC-SAFT parameters for alkanes, aromatics, and cycloalkanes at temperatures to 533 K and pressures to 276 MPa. The parameter values are a function of contributions from the various functional groups present and the nature of the various carbon atoms (aliphatic, aromatic, and naphthenic) comprising the molecule. Furthermore, when using second-order group contributions, it is possible to distinguish the differences in density among isomers. Density values are usually calculated to within +/- 1-2%. Isothermal compressibility values are calculated to within +/- 10%, isobaric heat capacity to within +/- 5%, and speed of sound to within +/- 4%.