Methanol molecules inside carbon nanotubes open to a liquid methanol reservoir are studied by molecular dynamics simulations. The way of filling is explored for a wide range of tube diameter size, from a large one revealing a 'bulk mode' to a small one revealing a 'monowire mode', in which the molecules are hydrogen-bonded one-dimensionally. Stemming from the coexistence of the hydrophobic and the hydrophilic groups, the formation of a methyl-hydroxyl 'biwall' along the CNT wall and a subsequent 'biwire' consisting of two methanol subwires running through the CNTs are observed to precede the monowire as the diameter size decreases. (C) 2012 Elsevier B.V. All rights reserved.