Densities for 1-propylpyridinium tetrafluoroborate, 1-butylpyridinium tetrafluoroborate, 1-butylpyridinium triflate, 1-butyl-3-methylpyridinium dicyanamide, and 1-octyl-3-methylpyridinium tetrafluoroborate are reported in a broad range of temperatures (283.15-333.15 K) and pressures (0.1-65 MPa). The pressure-volume-temperature behaviours of these fluids have been correlated successfully with the empirical TRIDEN equation; then, relevant derived properties such as the coefficient of thermal expansion, and the isothermal compressibility have been calculated. A comparison of the results has been carried out to analyse their properties in structural and energetic terms. (C) 2012 Elsevier B.V. All rights reserved.