Densities, ρ and speeds of sound, u of four benzylalkylammonium ionic liquids (ILs), namely, benzylmethylammonium propionate (BMAP), benzylmethylammonium hexanoate (BMAH), benzyldimethylammonium propionate (BDMAP) and benzyldimethylammonium hexanoate (BDMAH) with dimethylsulfoxide (DMSO) have been determined as a function of ILs concentration, ranging from (0.1 to 0.8) mol kg−1, at temperatures from 293.15 K to 328.15 K with 5 K interval and at atmospheric pressure. The apparent molar volumes, Vm, apparent molar isentropic compression, Ks,m and limiting apparent molar expansion, Em∞ of the ILs have been calculated from the experimental density and speed of sound data. The Redlich–Mayer type of equation was fitted to the apparent molar volume and apparent molar isentropic compression data, to evaluate apparent molar volume at infinite dilution Vm∞ and apparent molar isentropic compression, Km∞ at infinite dilution.