Group additivity values are presented which can be used to estimate standard heats of formation for a variety of gaseous fluorocarbons, chlorofluorocarbons, hydrofluorocarbons and hydrochlorofluorocarbons (molecules, radicals, diradicals and carbenes). Wherever these values cannot be obtained directly from standard heats of formation, they are estimated by requiring bond dissociation enthalpies to follow monotonic trends across homologous series of species. For cases where there is insufficient information to establish these trends, an alternative empirical procedure that stems from ab initio results is used. An estimate of the uncertainty in each group additivity value is provided.