Mass transfer properties of fluorinated polycarbonate siloxanes (PCS-F) for some gases and hydrocarbons depending on the chemical nature of the carbonate and siloxane blocks and the composition of the block copolymers have been investigated. As compared with poly(dimethylsiloxane)s, polycarbonate siloxanes, and methyltrifluoropropylsiloxane homopolymers, fluorinated polycarbonate siloxanes exhibit a higher separation selectivity alpha for CO2/N-2, CO2/O-2, and CO2/CH4. At a 30 wt % concentration of trifluoropropyl groups, PCS-F have alpha values of 4.9 and 17.8 for O-2/N-2 and CO2/CH4, respectively. The PCS-F copolymers exhibit a high resistance to hydrocarbons, retaining the mechanical properties in the swollen state.