Densities of pure 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide, [C(3)mpip][NTf2], and its mixtures with anisole or acetophenone were measured with a high-pressure densimeter at temperatures from 298.15 K to 348.15 K and pressures up to 50 MPa. The Tait equation was employed to represent pressure effect on the isothermal densities. The experimental results reveal that the excess volumes of (anisole + [C(3)mpip][NTf2]) and (acetophenone + [C(3)mpip][NTf2]) are all negative over the entire experimental conditions. In addition to an empirical generalized equation, the density data were also correlated quantitatively with the Flory-Orwoll-Vrij (FOV) and the Schotte equations of state. (C) 2012 Elsevier Ltd. All rights reserved.