The selectivity of adsorption of a component of a binary or a ternary gas mixture can be a complex function of equilibrium gas phase pressure, temperature and composition and it must be experimentally measured for reliable design of adsorptive gas separation processes. The results of a literature search (1995-2015) using the search engine 'Web of Science' for experimental data on binary and ternary gas adsorption selectivity and their estimation from the corresponding pure gas adsorption isotherms by Ideal Adsorbed Solution Theory (IAST) are summarized. The published data cover a large range of equilibrium gas phase conditions and adsorption systems having different adsorbate (molecular size, polarity) and adsorbent (energetic heterogeneity, polarity) properties. The estimation of selectivity by IAST vis a vis the experimental data was good to reasonable for certain systems, while the deviation was large for others. Potential reasons for such observations are discussed. (C) 2016 Elsevier B.V. All rights reserved.