Generally, researchers to study mass transfer of gas phase into liquid use pressure decay method, visual cell or pendant drop technique. Despite available data about CO2 solubility in oil, there are limited methods which allow to study interactions between fluids. In this paper, a newly developed acoustic pulse echo (APE) technique was applied to measure oil volume expansion factors in the presence of carbon dioxide in a pressure range of 2-6 MPa at a temperature of 297 K to cover most practical cases of interest for the vapor extraction process. With the APE technique, a wave is emitted from a piezoelectric transducer, and its reflection from the boundary is detected at a later time. As CO2 becomes soluble in the oil, the boundary between the fluids moves upward, thus affecting the travel time of the reflected wave from the fluid interface. Since volume changes are registered, the expansion factor can be evaluated. The experimental results show that the oil swelling factor increases with pressure; this clearly indicates that there are certain correlations between the oil swelling factor and the solubility of an oil-solvent system. The evidence for the validity of the acoustic technique was provided by comparing measured values with literature data. Compared to other investigatory approaches, the main advantage of this newly developed method is its ability to provide highly accurate swelling factor values for CO2/oil system. The method developed in this study can be serviceable for further and more complex investigations on gas-EOR experiments. (C) 2018 Elsevier Ltd. All rights reserved.