► Modeling IL densities and gas solubilities in imidazolium-based ILs with ePC-SAFT. ► Different modeling strategies for ILs were compared within PC-SAFT. ► Pure-IL densities could be predicted from 283 to 473K and up to 3000bar. ► The CO2 solubility in ILs could be predicted based on density-fitted parameters. ► The much lower solubility of CH4 compared to CO2 could be predicted. ePC-SAFT was used to investigate the density and gas solubilities in imidazolium-based ionic liquids (ILs) applying different modeling strategies. The ion-based strategy including a Debye–Hückel Helmholtz-energy term to represent the ionic interactions describes the experimental data best. For this strategy, the IL was considered to be completely dissociated into a cation and an anion. Each ion was modeled as non-spherical species exerting repulsive, dispersive, and Coulomb forces. A set of ePC-SAFT parameters for seven ions was obtained by fitting to reliable density data of pure ILs up to 1000bar with a fitting error of 0.14% on average. The model can be used to quantitatively extrapolate the density of pure ILs at temperatures from 283 to 473K and pressures up to 3000bar. Moreover, this strategy allows predicting CO2 solubilities in ILs between 293 and 450K and up to 950bar. Applying the same set of IL parameters, the much lower solubility of CH4 compared to CO2 can also be predicted with ePC-SAFT.