Experimental p-rho-T data obtained with a constant volume apparatus are reported for two ionic liquids with trihexyl(tetradecyl)phosphonium ([THTDP]) cation and bis(trifluoromethylsulfonyl)imide, [NTf2], and dicyanamide, [DCA], anion and for 1-hexyl-3-methylimidazolium hexafluorophosphate, [C6MIM][PF6]. The measurements were conducted at temperatures from (218 to 364) K and at nominal pressures of 1 MPa and from (10 to 50) MPa with a 10 MPa step. Thus, the temperature region covered with experimental p-rho-T data has been substantially extended to lower temperatures for all three substances. The expanded combined uncertainty at the 0.95 confidence level of the reported densities takes its maximum value at the lower end of the temperature interval of the data, namely 1.3 kg.m(-3) (1.3.10(-3)rho) for [THTDP] [NTf2], 0.6 kg.m(-3) (0.7.10(-3)rho) for [THTDP][DCA], and 1.8 kg.m(-3) (1.4.10(-3)rho) for [C6MIM][PF6]. The studied ionic liquids show a specific type of the temperature and pressure dependence of their internal pressure, different from that of molecular liquids such as water or aliphatic alcohols. In addition, experimental 0.1 MPa density data and air liquid surface tension data are reported for both phosphonium based ionic liquids obtained with the buoyancy method and the Wilhelmy plate method, respectively, at temperatures from (263 to 365) K.