The ionic liquid (IL) + CO2 system was studied for solubility measurement in three distinct [BETI] anion-based ILs: 1-ethyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide ([EMIM][BETI]), 1-butyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide ([BMIM][BETI]), and 1-hexyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide ([HMIM][BETI]) in the experimental ranges of 0.129.3 MPa and 303.2373.2 K. The present study shows the solubility of CO2 in several [BETI] anion-based ILs under specific experimental conditions and compares the effect of three cations: [HMIM], [BMIM], and [EMIM]. CO2 solubility data were measured by determining bubble (or cloud)-point pressures at targeted CO2 mole fractions. It was found that CO2 absorption abilities were placed in the following order: [HMIM][BETI] > [BMIM][BETI] > [EMIM][BETI]. Moreover, these three [BETI]-containing ILs were compared with previously published data for investigating the influence of the [BETI] anion. The result shows that the three [BETI] anion-based ILs have relatively higher solubility for CO2 than any other ILs discussed in this paper. These experimental results also show that the larger amount of the fluoro-alkyl group containing anion increases CO2 solubility. To correlate and calculate the resulting data, the following methods were used: the PR-EoS with one-fluid mixing rule and the modified LydersenJobackReid method. The overall absolute average relative deviation were 0.0172, 0.0246, and 0.0118 for CO2 + [EMIM][BETI], CO2 + [BMIM][BETI], and CO2 + [HMIM][BETI] systems, respectively.