Experimental measurements of gaseous second virial coefficients of haloalkanes and their liquid thermal conductivities and viscosities at saturated vapour pressure are reviewed and assessed. It is found that the Tsonopoulos equation provides a good representation of second virial coefficient data when the dipolar term is included, although the Weber equation generally gives an improved fit. Application of the square-well potential, with parameters forced to give a realistic ratio of the Boyle temperature divided by the critical temperature, is shown to provide an excellent data fit with values for molecular size and total attractive energy which exhibit a regular variation with change in molecular structure. Thermal conductivity and viscosity data of these compounds are satisfactorily fitted by equations developed at the National Engineering Laboratory in Scotland. The values of the coefficients in these equations depend on the extent of fluorine- or chlorine-substitution in chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), and on the length of the carbon chain in higher halogenated alkanes.