In a recent webinar we demonstrated how to model semicrystalline structures using the MedeA tools. In this presentation we use the same structures to calculate CO2 and CH4 sorption over a large range of pressures from 1 MPa to 40 MPa. To do this, we use a combination of Monte Carlo and Molecular Dynamics techniques iterated in cycles. With the CO2 and CH4 gas molecules thus sorbed in the polymer matrices, we use MedeA's molecular dynamics simulation tools to obtain the diffusion coefficients via Einstein's equation. The obtained sorption and diffusion coefficients fully describe the permeation properties of the polymer.