The influence of a controlled oxygen pressure on the metallization (by Al, Ag and Cu) of poly(ethylene terephthalate) (PET) has been investigated. The structure of the interfaces and of the bulk metallic films has been characterized using TEM. The laminate peel energy strength has been measured with a standard peel test. The most significant results concern the Al/PET laminates : (i) wet and dry adhesion are greatly improved if an oxygen partial pressure higher than 10(-5) mbar is introduced during evaporation of the him, and (ii) depending on the oxygen partial pressure, either metallic Al films with various grain size or amorphous aluminium oxide films are prepared. No significant improvement in adhesion is observed with an oxygen partial pressure (10(-6) to 10(-4) mbar) during the evaporation of Ag or Cu. These results are discussed in terms of the mechanism of chemical interaction at the metal-polymer interface. As chemical reactions with oxides or hydroxides are likely to occur with aluminium, the gas phase interaction would contribute to the oxidation process. Ag and Cu being much less reactive, another mechanism involving metal diffusion in the free volume of the polymer dominates and the presence of oxygen has almost no effect.