We present a unique bench scale apparatus for directly measuring volumetric gas storage capacities designed at UTRC. The apparatus construction avoids gas leakage, and the analysis of experimental data prevents leakage from inflating capacity measurements. Deliverable methane storage capacities (V-d/V-s) of adsorbents are evaluated directly from experiments with this apparatus rather than calculated from gravimetric adsorption capacities. We suggest that an adsorbent for methane storage should have an optimal pore volume consisting of pores ranging from 8 to 15 Angstrom, rather than a monodispersed 8 Angstrom pore size distribution as calculated by recent computer simulations. This interpretation is based on our modeling results and on the fact that physical activation usually produces an adsorbent with a polydisperse distribution of pore size. In general, ultra-micropores (<7 Angstrom) should be avoided and super-micropores (7-20 Angstrom) should be developed during adsorbent preparation. Ultra-micropores collect "cushion gas," thus reducing deliverable storage capacity. Super-micropores offer high methane adsorption densities and fast adsorption/desorption kinetics.