Surface tension data were measured by the Wilhelmy plate method for the binary mixtures containing an ionic liquid of the imidazolium dialkylphosphate family and water (methanol or ethanol) at 298.15 K and atmospheric pressure. The enthalpy of vaporization Delta H-g(l)m(o) and Hildebrand solubility parameter delta(H) for the pure components are estimated from the experimental data, and a perfect correlation is found between surface tension and specific cohesive energy per unit surface area for the imidazolium dialkylphosphate series ionic liquids (ILs). The surface tension as well as the surface tension deviation against the solution composition shows a remarkable difference between the mixtures of an IL with water and with alcohols, which is interpreted qualitatively by the delta H values of the corresponding pure components. Some ILs act as a surfactant in aqueous solution, but most of them more like a conventional nonelectrolyte component in the alcoholic solutions.