The adsorption of two small molecules in porous crystals presenting void volumes of different shapes (cavities of similar to 12 Angstrom diameter, channels of similar to 6 Angstrom diameter) is measured in a large range of temperatures and pressures. The data analysis shows off the difference in the intermolecular forces between N-2 and O-2 molecules; in condensed phases the molecule-molecule interaction is repulsive and it is more repulsive for N-2. The density of the adsorbed phase is compared with that of the liquid at three temperatures; that points out the confinement effect which is dominant in the channels.