Adsorption of vapors on a solid adsorbent, with a gas as the only mobile phase, defines gas–solid chromatography (GSC). Unlike gas–liquid chromatography, there is no liquid stationary film; retention is governed by the adsorption isotherm of the solute on carbon, molecular sieves, porous polymers, or inorganic oxides ^[1]. The same experiment that separates permanent gases and light hydrocarbons also yields adsorption isotherms and surface-energy parameters when the solid is the object of study ^[2]. Conceptual boundaries exclude gas–liquid (partition) chromatography, inverse gas chromatography when it is used solely as a surface-characterization tool without being identified as GSC, and liquid–solid chromatography. Essential features are a gaseous carrier, a solid adsorbent packing or porous-layer wall, and a temperature at which the solutes remain volatile while adsorption remains reversible. Retention of carbon monoxide, light hydrocarbons, and related gases in packed or multi-bed adsorbent columns follows adsorption rather than partition into a liquid film ^[3].