The thermodynamic behaviour of imidazolium based ionic liquids (ILs), 1-butyl-3-methylimidazolium chloride [C(4)mim][Cl]; 1-octyl-3-methylimidazolium chloride [C(8)mim][Cl], and 1-butyl-3-methylimidazolium methylsulfate [C(4)mim][C(1)OSO(3)] in ethylene glycol [HOCH(2)CH(2)OH] (EG) have been investigated over the whole composition range at T = (298.15 to 318.15) K to probe the interactions in bulk. For the purpose, volumetric properties such as excess molar volume, V(m)(E), apparent molar volume, V(phi,i), and its limiting values at infinite dilution, V(phi,i)(infinity), have been calculated from the experimental density measurements. The molecular scale interactions between ionic liquids and EG have been investigated through Fourier transform infrared (FTIR) and (1)H NMR spectroscopy. The shift in the vibrational frequency for C-H stretch of aromatic ring protons of ILs and O-H stretch of EG molecules has been analysed. The NMR chemical shifts for various protons of inns or EG molecules and their deviations show multiple hydrogen bonding interactions of varying strengths between RTILs and EG in their binary mixtures. (C) 2011 Elsevier Ltd. All rights reserved.