The reforming catalytic properties of tungsten and molybdenum dioxides have been interpreted in terms of a bifunctional mechanism. A stable XO2 (X = W, Mo) has been obtained following the reduction of XO3 by hydrogen for 4h at 400 degreesC for Mo and 460 degreesC for W. A relatively high selectivity lip to 100% in isomerization products for the hexanes were obtained at reaction temperatures of 280 degreesC in the case of MoO2 and at 300 degreesC for WO2. Titanium dioxide, TiO2, was chosen as the appropriate support on the basis of its electronic structure which enables to avoid a strong metal-support interaction with the active XO2 phase.