Many separation processes in petrochemical and refining industries are applied to close boiling point compounds and/or azeotropic mixtures which make difficult the application of simple distillation, requiring alternative separation processes. Ionic liquids, with their unique and tunable properties, may constitute an advantageous alternative as extractive solvents in separation processes that involve hydrocarbon systems. In this work, a review on the experimental data available for ternary systems composed of ionic liquids and hydrocarbons is reported. The gathered information was shown to be essential in the understanding of the molecular interactions and of the effect of the various structural features of both the ionic liquids and the hydrocarbons on their phase behavior, allowing the development of guidelines for the choice of the most suitable ionic liquid for hydrocarbon separation. To be able to carry out the design and selection of new and improved ionic liquids, the development of predictive models and their validation is required, since the experimental screening of the huge number of potential ionic liquids is not feasible. In this context, the ability of COSMO-RS (COnductor-like Screening MOdel for Real Solvents) as a predictive tool to describe the liquid–liquid equilibria of ternary systems composed of ionic liquids and hydrocarbons, is evaluated. The results obtained with COSMO-RS testify its ability for the qualitative, and in some cases the quantitative, description of the phase behavior of the systems studied.