The sorption of propylene and propane in solid polymer electrolytes based on blends of poly(ethylene oxide) (PEO) and silver nitrate, AgNO3, silver triflate, AgCF3SO3, silver trifluoroacetate, AgCF3CO2. or silver tetrafluoroborate, AgBF4, are reported. These solid polymer electrolytes exhibit preferential sorption for propylene over propane due to complexation of propylene with silver ions in the polymer matrix and reduced propane solubility in the solid polymer electrolyte films relative to that in PEO alone. The order of olefin solubility in blends containing 1 mol of silver ions per mole of ethylene oxide (EO) units is: AgBF4 >> AgCF3SO3 > AgCF3CO2 > AgNO3. At 35 degreesC and 40 cmHg pressure, a PEO/AgBF4 film containing 1 mol of silver ions per mole of EO sorbed 5.3 g propylene but only 0.083 g propane per 100 g of solid polymer electrolyte. AgBF4 is highly soluble in PEO and completely disrupts polymer crystallinity even at low salt concentration (approximately 10 wt.%) without significantly altering the glass transition temperature. Other silver salts (e.g. AgNO3) do not dissolve completely in PEO and are much less effective at promoting enhanced olefin solubility.