CO2 solubility coefficient vs. CO2/CH4 solubility selectivity (at infinite dilution) data of all polymers tested for CO2-CH4 mixed-gas sorption at 35 °C [11,15,18,20,22,23,48]. CO2/CH4 solubility selectivities were obtained from linear interpolation of CO2 mixed-gas solubility coefficient vs. CH4 mixed-gas solubility coefficient data or from pure-gas uptake data via DMS model equations—see the discussion in the Supporting Information and data values in Table S2. CO2 solubility coefficients were estimated from experimental data of pure-gas CO2 uptake. The 2014 CO2/CH4 solubility upper bound was discussed elsewhere [47].