The adsorption of methane gas on isolated single-walled carbon nanotubes (SWNT) and idealized carbon slit pores at 303 K is studied by nonlocal density functional theory (DFT). On a per weight basis, total excess adsorption on the internal and external surfaces of an isolated SWNT exceeds that for the idealized slit pore with the same size, although the adsorption capacity of the interior of SWNT is less than that for the silt pore geometry. It is also found that methane adsorptions inside and outside the isolated SWNT are enhanced by methane molecules adsorbed on the opposite surface. (C) 2002 Elsevier Science B.V. All rights reserved.