In order to examine the impact of the flexibility of kerogens' microporosity on the transport of adsorbed CO 2 , we develop a free volume model that notably accounts for adsorption-induced swelling exhibited by flexible kerogen structures. We first show that, for CO 2 compared to CH 4 at constant fluid molar loading and in the same conditions, the atomistic model of microporous kerogen we use exhibits slightly less swelling upon adsorption. This swelling comes with an increase in the free volume accessible to the CO 2 molecules, which can then diffuse faster when the fluid loading increases, without introducing significant collective effects on the transport properties. Consequently, transport can be considered diffusive and the self-diffusion coefficient can be used as a proxy for the collective diffusion (or transport) coefficient. Finally, as previously demonstrated for CH 4 , a free volume model based on the Fujita-Kishimoto theory describes the transport enhancement with CO 2 fluid loading. Although CO 2 interacts i more strongly than CH 4 , the parameters of the free volume models for both fluids are shown to be similar. Together with the diffusive nature of transport, it suggests an even broader applicability of the model to the transport of light alkanes and mixtures, thus greatly simplifying transport modeling for geological applications such as carbon sequestration in shales.