NOVELTY - Carbon molecular sieve (Ia) comprises: (a) greater than or equal to 99 wt.% of carbon; (b) many micropore sidewalls forming interconnected micropores having internal diameters of 10-20 Angstrom , where the micropore sidewalls comprise 5-40% of the total surface area of the carbon molecular sieve; and (c) many ultramicropore sidewalls forming interconnected ultramicropores having mean internal diameters of 3-10 Angstrom and individual internal diameters within 0.5 Angstrom of the mean internal diameter, where the ultramicropore sidewalls comprise 10-60% of the total surface area of the carbon molecular sieve.    USE - The carbon molecular sieve is useful for: storing molecular hydrogen gas; and adsorbing or separating molecular gas comprising hydrogen, helium, xenon, krypton, methane, ethane, carbon monoxide and/or carbon dioxide from a mixture of gases containing the molecular gas (all claimed).    ADVANTAGE - The carbon molecular sieve: is non-toxic; is easy to handle; does not require excessive additional equipment to store and release hydrogen; and is relatively insensitive to the presence of contaminants in the hydrogen to be stored.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a carbon molecular sieve (Ib) comprising: (d) a spherical particle comprising greater than or equal to 99 wt.% of carbon, where the particle has a diameter of 2-1000 mu m; component (b) as above per se; (e) many ultramicropore sidewalls forming ultramicropores having a mean internal diameter of 3-7 Angstrom and individual internal diameters within 0.5 Angstrom of the mean internal diameter, where the ultramicropore sidewalls comprise 10-60% of the total surface area of the carbon molecular sieve;    (2) method (IIa) of forming a carbonaceous adsorbent comprising: (f) polysulfonating a microporous polymer ion exchange resin to produce a polysulfonated ion exchange resin; and (g) pyrolyzing the polysulfonated ion exchange resin to produce the carbonaceous adsorbent;    (3) method (IIb) of forming a carbon molecular sieve comprising: steps (f) and (g) as above per se; (h) activating the carbonaceous adsorbent to form an activated carbonaceous adsorbent; and (i) pyrolyzing the activated carbonaceous adsorbent to form the carbon molecular sieve;    (4) forming a carbon molecular sieve comprising: contacting a porous polymer ion exchange resin with fuming sulfuric acid (100-2000 wt.%, based on the ion exchange resin) at 100-180 degrees C for 5-72 hours to form a polysulfonated ion exchange resin; pyrolyzing the polysulfonated ion exchange resin at 300-1200 degrees C for 15 minutes to 2 hours to form a carbonaceous adsorbent; contacting the carbonaceous adsorbent with a physical activation gas comprising steam, oxygen and/or carbon dioxide at 500-1200 degrees C, to form an activated carbonaceous adsorbent; and pyrolyzing the activated carbonaceous adsorbent at 560-1300 degrees C for 15 minutes to 2 hours, to form the carbon molecular sieve;    (5) storing molecular hydrogen gas, comprising contacting the molecular hydrogen gas with the carbon molecular sieve at a pressure of 1-1000 psig, where the carbon molecular sieve comprises ultramicropores having internal diameters of 4.5-5.5 Angstrom ; and    (6) separating molecular gas comprising hydrogen, helium, xenon, krypton, methane, ethane, carbon monoxide, or carbon dioxide from a mixture of gases containing the molecular gas, comprising contacting the mixture of gases with the carbon molecular sieve particle at a pressure of 1-1000 psig, where the carbon molecular sieve comprises ultramicropores having internal diameters of 4.5-5.5 Angstrom .