This chapter provides a comprehensive analysis of the sorption effects of oxy-fuel-relevant species and the particle pore structure evolution during pyrolysis and char conversion. The methodology considers physisorption measurements and suitable density functional theory models for pore surface area and volume analysis. Furthermore, the mass transport of oxy-fuel-relevant species in the porous fuel particles was investigated by adsorption kinetic measurements. Applying suitable adsorption kinetic and diffusion models based on the experimental data provides mass transport properties, which are intended to be used in common char conversion and combustion models. A novel pore structure-dependent adsorption kinetic (PSK) model is presented incorporating a physically sound description of the time-dependent intraparticle mass transport process. Moreover, incorporating relative pressure adsorption kinetic data, a relative pressure (RP)-PSK model is developed enabling the prediction of mass transport processes, which depend on a relative pressure difference of oxy-fuel components in the bulk phase and the gas phase in the intraparticle structure.