In order to deep insight on the molecular interactions between thiophene (TS) and some imidazolium based ionic liquids, density, speed of sound and refractive index of binary liquid mixture of TS with octane, 1-hexyl-3-methylimidazolium bromide [HMIm] Br, and 1-octyl-3-methylimidazolium bromide [OMIm] Br at T = (288.15 to 303.15) K and at atmospheric pressure has been measured in dilute region of TS. Various thermophysical parameters including partial molar volumes, (v) over bar (m,i), apparent molar volumes, V-phi, standard partial molar volumes V-phi(0), transfer volume of thiophene from octane to ionic liquid mixtures, Delta V-tr(phi)0, partial molar isentropic compressibility, k(phi)(0), excess molar volumes, V-E, excess partial molar volumes, (v) over bar (E)(m,i), molar refractions, R-D have been calculated using these data. The densitometric and refractometric non-intrinsic contribution to the partial molar volume, theta(d) and theta(r) have been obtained using the measured experimental data. Also, interaction volume, V-int, and cavity volume, V-cav, have been calculated from scaled particle theory (SPT). The results demonstrate that ionic liquids used in this study do not interact effectively with thiophene. (C) 2016 Elsevier Ltd. All rights reserved.