Abstract  Density and speed-of-sound data for 1-propyl-3-methylimidazolium bromide ([C₃mim][Br]) + acetonitrile (MeCN), [C₃mim][Br] + dimethylformamide (DMF), and [C₃mim][Br] + dimethylsulfoxide (DMSO) binary mixtures in the dilute concentration region are reported at T = (288.15 to 308.15) K. From these data, apparent molar volume, isentropic compressibility, excess molar volume, and isentropic compressibility deviation values have been calculated. Negative deviations from the ideal behavior of both molar volume and isentropic compressibility have been observed for all systems investigated in this study. It has been found that deviations from ideal behavior for the [C₃mim][Br] + MeCN system are larger than those for the [C₃mim][Br] + DMF system which, in turn, are larger than those for the [C₃mim][Br] + DMSO system. The results have been interpreted in terms of ion–dipole interactions and structural factors of the ionic liquid and investigated organic solvents.