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Separation of a methane/nitrogen gas mixture was investigated by means of carbon molecular sieves (CMS) obtained from a newly discovered "green" resource: Salix viminalis. This plant grows quickly, yields hard wood and is frequently cultivated for energy purposes (renewable green fuel). Unconventional applications such as charcoal fabrication using this sort of wood are very rare. Carbonization of the wood (1-3 h, 600-700°C) yields carbons with a very narrow pore size distribution (determined by N2 adsorption at -196°C) resembling a perfect CMS. The diameter of most pores (ca. 0.8 nm) is comparable to the size of simple molecules, thus enabling separation. The sieving effect was proven in an industrially important process of CH 4 /N 2 separation at 30-70°C. Despite relatively minor differences of the size of the molecules, the experiment demonstrated that separation factors are placed in the range 3.64-10.20. Additional experiments involving krypton proved that the separation mechanism is based on a geometric factor i.e. the known size and shape of the molecules under separation