Porous anodic films on zirconium, formed potentiostatically in fluoride/glycerol electrolytes of different water content, are examined by ion beam analysis and analytical electron microscopy for the purpose of understanding the generation of nanotubes. Cross-sections of the films, prepared by focused ion beam, showed the presence of oxide-based nanotubes within a fluoride-based matrix. The atomic ratio of fluorine to oxygen in the films decreases with the addition of water to the electrolyte and with increase of the potential. The compositions and morphologies of the films, and their dependence on the anodizing conditions, are discussed in relation to the growth mechanism of the films. (C) 2011 Elsevier Ltd. All rights reserved.