The quasi-symmetric top molecule approach proposed previously [J. Koput, J. Mol. Spectrosc. 104, 12–24 (1984)] to calculate vibration-rotation energy levels of a CH 3XY molecule is used to study the COD bending-torsion-rotation energy levels of monodeuterated methanol, CH 3OD. The available 150 transition frequencies (microwave, millimeter wave, and infrared data) have been fitted and the barrier to linearity of the COD skeleton has been found to be about 7000 cm −1. The effective barrier to internal rotation in the ground state has been determined to be 365.79 cm −1 and that in the first excited state of the COD bending mode has been predicted to be 380.62 cm −1.