High pressure densities at (10200) MPa over a range of temperatures and atmospheric pressure viscosities at (293373) K for three ionic liquids (ILs) that are able to dissolve biomass, 1-ethyl-3-methylimidazolium methylphosphate ([emim][MP]), 1-ethyl-3-methylimidazolium diethylphosphate ([emim][DEP]), and 1-butyl-3-methylimidazolium acetate ([bmim][Ac]) are reported. Densities of the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) were measured at the same conditions to verify the apparatus and to extend the range of present data. The high pressure densities of [emim][MP] and [emim][DEP] are newly measured in this work. Combined expanded uncertainties of densities for [emim][MP], [emim][DEP], [bmim][Ac], and [bmim][Tf2N] were estimated to be 1.5 kg center dot m3, 1.4 kg center dot m(3), 1.4 kg center dot m3, and 1.7 kg center dot m(3), respectively. The Tait equation could correlate the experimental density data to within 0.03 % of average relative deviation. The derivative properties, isobaric expansivity, and isothermal compressibility were calculated using the Tait equation and it was observed that the isobaric expansivity decreased with increasing temperature. The trend of the isobaric expansivity and isothermal compressibility with temperature were in accordance with the theory of corresponding states using methanol for comparison.