Shale is an increasingly viable source of economic quantities of natural gas worldwide. Most of the gas is contained within the fine pores, thus characterizing accessibility and structure of pores is critical for understanding fluid (petroleum and water) flow and storage within these reservoirs. We propose to examine the pore accessibility of two Marcellus Shale samples to CO2 and CH4 in the new high-pressure cell. Each sample will first be pressurized with CO2 at 25 and 40 bar at 25°C for comparison to our previous study (Stefanopoulos et al. 2017). Then we will adsorb CD4 in the samples at zero contrast pressures to quantify accessible and inaccessible porosity to CH4. This work has direct application to resource recovery as closed gas-filled pores have no access to the flow network. Also closed pores are not available for storage sites in CO2 sequestration projects.