Ionic liquids are promising solvents for extracting CO2 from H-2, N-2 and O-2 using the absorption separation method. Solubilities of these gases in 1-hexyl-3-methylimidazolium tris( pentafluoroethyl) trifluoropho sphate ([HMIM][eFAP]) were determined using an isochoric saturation method. Experimental result indicates that solubilities of H-2, N2 and O-2 in [HMIM][eFAP] are much lower than that of CO2. The performance of [HMIM][eFAP] in separating CO2 from N-2, H-2 and O-2 can be improved by decreasing the temperature. Based on the solubility data, the ideal selectivities of CO2/N-2, CO2/H-2, and CO2/O-2 in different ionic liquids were calculated and the effect of the ionic liquid structure on them were investigated. (C) 2016 Elsevier Ltd. All rights reserved.