A previously non-described trimer with a C-H...O hydrogen bond has been characterized as minimum at several computational levels. This conformer allows a complete assignment of the experimental infrared cavity ringdown laser absorption spectrum (IR-CRLAS) in the O-H stretch region. B3LYP/6-311++G(d,p) charge densities of the methanol dimer and trimers analyzed with the atoms in molecules (AIM) theory indicate the hydrogens of the methyl group play a significant role on the stabilization of these clusters. On the contrary, their cooperative effects can be numerically reduced to those exhibited by the OH groups. (C) 2003 Elsevier B.V. All rights reserved.