Publisher Summary This chapter discusses the control of supercritical gases with the help of solid nanospace. There are many important supercritical gases whose critical temperature is lower than an ambient temperature. Some of these gases are O2, N2, NO, CO2, CO, H2, and CH4. These supercritical gases have been deeply associated with gas separation, gas storage, catalysis, supercritical extraction, supercritical drying, pollution control, and life science. The supercritical gases can be controlled by the adsorption of micropores. The most representative microporous solids are zeolites and activated carbons. Both have different pore structures and adsorptive properties. Activated carbon has abundant micropores and their adsorption field can be approximated by the graphite-slit space model. The depth of the potential well of nanospace in the model is not enough for a supercritical gas to be sufficiently adsorbed, but chemical modification of the pore walls can deepen the potential well for the supercritical gas, leading to a marked micropore filling. Supercritical gas molecules tend to be adsorbed in micropores of the deep-potential well, and their intermolecular interaction has been enhanced to form an organized structure, as if molecules were compressed by a high pressure.