A carbon pyrolyzate adsorbent is described that is selective for carbon dioxide in contact with gas mixtures including carbon dioxide and methane. The adsorbent has a carbon dioxide adsorbent capacity at 1 bar pressure of greater than 50 cm3 carbon dioxide per gram of adsorbent at 273K, a methane adsorption capacity at 1 bar pressure of less than 35 cm3 methane per gram of adsorbent at 21° C., and a bulk density of greater than 0.55 gram per cubic centimeter of volume. Such adsorbent can be utilized, for example, for biogas upgrading, natural gas purification, coal bed methane purification, and refining operations.