Thermophysical properties viz, surface tension, viscosity, density, and ultrasonic velocity of three ionic liquids 1-butyl-3-methyl imadazolium octyl sulfate [BMIM][OcSO(4)], 1-butyl-3-methyl imadazolium hexafluorophosphate [BMIM]-[PF6], and 1-ethyl-3-methyl imadazolium methanesulfonate [EMIM][MeSO3] have been measured in a wide temperature range. Experimental data so obtained have been used to calculate isentropic compressibility, isothermal expansion coefficient, surface entropy, surface enthalpy, and critical temperature (temperature where the distinction between liquid and gas phase vanishes and the surface tension tends to zero). Structure property correlation for different ILs is also discussed.