The possible relationship between the superstructures in hydrogen molybdenum bronzes and charge density wave (CDW)-type instabilities of their Fermi surface (FS) is analyzed. It is shown that, depending on structural details, two-dimensional, one-dimensional and quite localized bands can be in competition at the bottom of the t(2g)-block band structure changing the shape of the FS. It is suggested that the topology of the FS is not the main driving force for the adoption of the superstructures but may be at the origin of some conductivity anomalies of these phases. (C) 2003 Elsevier B.V. All fights reserved.