Increased reductions of statutory sulfur content on fossil fuels as gasoline or diesel have led to intense research into all possible methods of desulfurization. With the aim to study [C(8)mim][BF4] ionic liquid as extraction solvent for desulfurization, the phase equilibria of different ternary systems involving hydrocarbons present in gasoline formulations, thiophene, and [C(8)mim][BF4], were obtained experimentally. Potential interest of this ionic liquid for desulfurization was confirmed by the phase equilibria determined. As design of a multistage separation process requires knowledge of phase equilibria, simultaneous correlation of liquid-liquid equilibrium data was done using the nonrandom two liquid (NRTL) activity coefficient model. A gasoline formulation was simulated as a mixture of n-hexane, cyclohexane, iso-octane, and toluene with thiophene and dibezothiophene as sulfur-components, and its desulfurization was performed by multistage extraction using the ionic liquid in three successive stages. (c) 2007 American Institute of Chemical Engineers AIChE J, 53: 3108-3115, 2007.