A statistical analysis of experimental vibro-roto-torsional energy levels of CH3OH, CD3OH, CH3OD, (CH3OH)-C-13 and (CD3OH)-C-13 molecules is performed, calculating the nearest neighbor spacing level distribution and the Dyson-Metha Delta(3)(L). The interactions among the molecular internal motions are clearly proved by the departure of the statistics from the regular spectral behavior, in particular for the CH3OD molecule, for both the NNLSD and the Delta(3)(L). Increasing the torsional number n, an increasing in the irregularity of the spectra is also observed, accounting for a stronger interaction among the internal and global rotation. Strong differences are seen in the statistics of the various isotopomers, claiming for a future more accurate and conclusive study of the isotopic dependence in the global molecular energy levels dynamics. (C) 2003 Elsevier B.V. All rights reserved.