On purpose of studying the regulations and prediction methods of volume expansion of CO2 + crude oil, eleven hydrocarbon components were selected to represent crude oil. Then, Constant Component Expansion (CCE) experiments were carried out with the hydrocarbon components and different molar fractions of CO2. According to the results, it was obviously that hydrocarbon components could expand the volume because of mixing the CO2. However, the expansion degree was largely influenced by the hydrocarbon properties. Therefore, a new parameter named the molar density was proposed to characterize these influences. The study found that hydrocarbon swelling factor and molar density were strict linear relationship. Based on this regulation and additional theoretical derivation, a prediction model was established to calculating volume expansion degree of CO2 + crude oil. With the experimental results of reservoir oil from CQ oilfield, it was turned out that the prediction model could successfully and precisely calculate crude oil swelling degree. (C) 2017 Elsevier B.V. All rights reserved.