Liquid-liquid equilibria in binary mixtures of halogenated benzene (chlorobenzene, bromobenzene, and iodobenzene) with ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim]-[Tf(2)N]), have been measured using a volumetric method over a temperature range from about (293 to 373) K. A general trend between the molecular size of the solute (monohalogenated benzene) and the immiscibility gap was discovered; the larger the size, the wider the gap. No correlation with the dipole moment exists, although other intermolecular interactions (higher-order moments, pi-electron effects, and hydrogen bonding) may also play a role. The excess molar volumes range from (-1 to -5) cm(3).mol(-1); the magnitudes are larger than those of ordinary liquid solutions. Observed LLE are well correlated by use of the nonrandom two liquid (NRTL) solution model.