Abstract: In this paper, experiments were carried out to investigate the retention of liquid hydrocarbons in kerogen type I. The study focuses on the mudstone from the Lucaogou Formation in the Junggar Basin of China. To prepare samples of kerogen with varying degrees of maturity, artificial pyrolysis was used. Swelling experiments with three different types of liquid hydrocarbons were then conducted. The results revealed that the peak swelling adsorption capacity of type I kerogen for liquid hydrocarbons occurred at Easy%Ro = 1.07. Additionally, the kerogen showed a selective ability to retain aromatic hydrocarbons throughout the entire process compared to alkane. The order of hydrocarbon expulsion from source rocks was established as follows: short-chain alkanes > cycloalkanes/long-chain alkanes > aromatics with alkyl groups > polycyclic aromatic hydrocarbons. This study also developed a model for evaluating the swelling capacity of kerogen. This model was capable of evaluating the total swelling state of liquid hydrocarbons without considering the adsorption state, which was not possible in previous experimental work. According to this model, the swelling ability of long-chain alkanes and polycyclic aromatic hydrocarbons in type I kerogen was high, while the swelling ability of cycloalkanes was weak, and most of them existed in the form of adsorption. This study suggests that paraffin and asphaltenes may affect the expulsion of shale oil and heavy oil in the form of swelling state, particularly in immature source rocks. This finding provides a new direction for research on hydrocarbon source rock evaluation and unconventional oil exploration.