The isothermal densities of pure ionic liquids, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, [C(4)mim][NTf2], and its mixtures with anisole or acetophenone were measured by using a vibrating tube densimeter over temperatures ranging from (298.15 to 348.15) K and pressures from (0.1 to 50) MPa. The Tait equation was used to correlate the density data and accurately represents densities varying with pressure at given temperature and composition. The excess volumes were calculated from the experimental data and found that those are all negative, except for (acetophenone + [C(4)mim][NTf2]) at 298.15 K with containing acetophenone of 0.1 in mole fraction. The modified Redlich-Kister was applied to correlate the excess volumes. The Flory-Orwoll-Vrij (FOV) and the Schotte equations of state were also employed to correlate the density data over entire experimental conditions. (C) 2013 Elsevier Ltd. All rights reserved.