In this work, phase equilibrium data for the systems 1-ethyl-3-methylimidazolium diethylphosphate ([emim][DEtPO4]) or 1-ethyl-3-methylimidazolium ethylsulfate ([emim] [EtSO4]) dibenzothiophene (DBT) + n-dodecane at 25 and 40 degrees C and atmospheric pressure (approximate to 95 kPa) were determined by refractometry. DBT and its derivatives represent the most difficult diesel sulfur pollutants to remove by the conventional process of hydrodesulfurization. These systems present not only liquid-liquid equilibrium (LLE) but also solid-liquid (SLE) and solid-liquid-liquid equilibrium (SLLE) regions. The LLE data were used to analyze the DBT extraction from n-dodecane as model diesel oil. DBT distribution coefficient, solvent selectivities, and extraction data indicate that [emim][DEtPO4] is a better solvent for extractive desulfurization of n-dodecane than [emim] [EtSO4]. The Hand and Othmer-Tobias correlations present R-2 > 0.97 for all systems. The nonrandom two-liquid model was used to correlate PSI data and shows root-mean-square deviations <0.1%.