A biaxially oriented polyester film comprising polyester and at least one hydrolysis stabilizer selected from a glycidyl ester of a branched monocarboxylic acid, wherein the monocarboxylic acid has from 5 to 50 carbon atoms, wherein said hydrolysis stabilizer is present in the film in the form of its reaction product with at least some of the end-groups of said polyester, and wherein said reaction product is obtained by the reaction of the hydrolysis stabilizer with the end-groups of the polyester in the presence of a metal cation selected from the group consisting of Group I and Group II metal cations.