Non-ideal behaviour of the room temperature ionic liquids (RTILs), 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4]; 1-octyl-3-methylimidazolium tetrafluoroborate [omim][BF4] and 1-butyl-3-methylimidazolium octylsulfate [bmim][C8OSO3] in ethylene glycol [HOCH2CH2OH] (EG) have been investigated over the whole composition range at T = (298.15 to 318.15) K. For the purpose, volumetric properties such as excess molar volumes, V-m(E), apparent molar volumes, V-phi,V-i, partial molar volumes, (V) over bar (m,i) excess partial molar volumes, (V) over bar (epsilon)(m,i) and their limiting values at infinite dilution V-phi,i(proportional to), and (V) over bar (proportional to)(m,i), (V) over barV(m,i)(E,proportional to) respectively have been calculated from the experimental density measurements. The V-m(E) results have been analyzed using the Prigogine-Flory-Patterson (PFP) theory. PFP theory has satisfactorily explained the volumetric behaviour of the binary mixtures. Refractive index measurements at 298.15 K have been used to calculate the deviations in refractive indices Delta(phi)n and the deviation of molar refraction A,R from their respective ideal values. Refractive index results have been correlated with volumetric results, and have been interpreted in terms of molecular interactions. Excess properties are fitted to the Redlich-Kister polynomial equation to obtain the binary coefficients and the standard errors. (C) 2008 Elsevier Ltd. All rights reserved.