The residual oil saturation determination is critical for the performance evaluation of any Enhance Oil Recovery (EOR) methods. The existing residual oil saturation determination methods are mainly based on solvent extraction. However, because the quality of the extracted residual oil and the remaining spent rock samples have not been examined before, this study investigates the accuracy of two commonly used solvent extraction methods for the residual oil saturation determination extracted from the spent rock samples of Steam Assisted Gravity Drainage (SAGD) and Solvent-SAGD. The results of the commonly used solvent extraction methods were compared with a new thermal method. It has been found that the thermal method provides more accurate results than solvent extraction method because the reservoir clays interact with residual oil and solvent methods cannot successfully separate the residual oil from reservoir rock. Therefore, a significant amount of clay is detected in the extracted residual oil through solvent extraction. Moreover, this study reveals that among the saturates, aromatics, resins, and asphaltenes fractions of residual oil, the aromatics fraction is responsible for the clay-asphaltene interaction and the resins content reduces this interaction. Because the solvents used to separate residual oil from rock samples are in general strong aromatic solvents, the existing solvent extraction methods fail to determine the residual oil saturation amount accurately. (C) 2016 Elsevier Ltd. All rights reserved.