The present invention relates to the use of a product obtainable by the reaction of an alkoxylated fatty amine with a dicarboxyhc acid derivative, followed by partial or total quaternization of the reaction product obtained; or by reacting a product with a dicarboxylic acid derivative, followed by partial or total quaternization of the reaction product obtained. The product consists of >60% w/w of oligomers/polymers with at least two alkoxylated amine units and one or more diacid/acid anhydride unit or >50% w/w of oligomers/polymers with at least two alkoxylated amine units and two or more diacid/acid anhydride units; as a corrosion inhibitor for metal surfaces. The invention also relates to a method for protecting a metal surface from corrosion by contacting the metal surface with said corrosion inhibitor.