The solubility of methane (CH₄) in ionic liquids (ILs) is required in order to develop processes involving CH₄, such as methane conversion and CO₂/CH₄ separation from natural gas or biogas processes. Nevertheless, the solubility of CH₄ in ILs is still very rarely achieved and, consequently, fundamental knowledge about the factors that govern the solubility are still poorly understood. Therefore, this work aims to extend the solubility data of CH₄ in various ILs and to gain some insights into the factors at a molecular level that play a role in the solubility process through experimental and computational modelling using Conductor-like Screening Model for Real Solvent (COSMO-RS). The solubility of CH₄ in 17 commercial ILs was measured experimentally at four different temperatures (298.15 to 343.15 K) and pressures up to 8 MPa. The large number of ILs studied allows the study of the impact of the cation and anion head group and the alkyl chain length on the solubility of CH₄. From the experimental solubility data collected, Henry's law constant (K_H) values were calculated. The results show that the solubility of CH₄ increases with decreasing temperature and increasing pressure. The solubility of CH₄ can also be enhanced by increasing the alkyl chain length of the IL cation or anion. Despite the inability of COSMO-RS to make quantitative predictions, the model is able to predict accurately the impact of the IL cation head group, anion, and alkyl chain length on the solubility of CH₄. Good correlation between the electrostatic – misfit energy, H_E,MF, of CH₄ and the experimentally calculated K_H values was obtained (R² = 0.932). This correlation indicates, for the first time, that the electrostatic – misfit energy arising from the repulsive interaction of CH₄ plays a dominant role in determining its solubility in ILs. In addition, it is shown that the IL size and van der Waals forces only have marginal influences on the solubility of CH₄. The experimental and computational modelling results in this work could pave the way to designing ILs as a medium for gas absorption and separation involving CH₄.