Gas-phase, NMR spectroscopy has been applied successfully in measuring pure- and mixed-gas equilibria on, a 5A adsorbent for carbon monoxide, methane, and nitrogen. The reliability of the technique is established. by comparing data collected here to pure-gas isotherms measured at 23 degreesC by standard volumetric expansion techniques in the pressure range of 0.5-5 atm. Mixed-gas equilibria,data for binary gas mixtures as well as the ternary gas mixture are compared with predictions based on heterogeneous ideal solution adsorption theory analysis.