Abstract: The application discloses a transparent, biaxially oriented polyester film having a base layer of at least 80% by weight which is composed of at least a thermoplastic polyester, and having at least one cover layer, wherein the cover layer is composed of a polymer or a mixture of polymers which comprises at least 40% by weight of ethylene 2,6-naphthalate units and optionally up to 60% by weight of ethylene terephthalate units and/or optionally units from aliphatic, cycloaliphatic or aromatic diols, and/or optionally aliphatic, cycloaliphatic and aromatic dicarboxylic acids, with the proviso that the T.sub.g 2 value of the polyester film is above the T.sub.g 2 value of the base layer but below the T.sub.g 2 value of the cover layer. The film has low atmospheric oxygen transmission. It is particularly suitable for packaging applications, specifically for packaging foodstuffs and other consumable items.