The activity coefficients at infinite dilution, gamma(infinity)(i), for 16 organic solutes: alkanes, alkenes, and alkyl benzenes in the ionic liquid 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM] [DEP]) have been measured by the gas-liquid chromatographic method. The measurements were carried out in the temperature range of (303.15 to 343.15) K. The partial molar excess enthalpies at infinite dilution, H(i)(E,infinity), of the solutes in [EMIM] [DEP] were also derived from the temperature dependence of the gamma(infinity)(i) values.