The adsorption isotherms of 16 halocarbons have been obtained in the mid to high range of pressures and at room temperature on a zeolite-like nanoporous carbon molecular sieve Carbosieve G (CSG). All the isotherms display Type I structure in the range investigated. The agreement between the pore volume of the adsorbent calculated based upon the liquid densities of the one-carbon, C 1 , halocarbons at room temperature and that determined from the nitrogen adsorption isotherm obtained at 77 K is good. The capacity of CSG for these C 1 molecules ranges between 4.7 and 7.5 mmol/g. For the larger two-carbon species, C 2 , the adsorption is lower, in the range from 3.1 to 4.7 mmol/g. A plot of these equilibrium capacities versus the molecule size shows how the extent of adsorption varies with molecule size. The pores with sizes in the near vicinity of 5 9 are found to predominate, a result which agrees well with pore size determinations made earlier by other means.