Abstract: The use of synthetic polymer in combination with an organic corrosion inhibiting compound having at least one unsaturated carbon-carbon bond, preferably selected from the group of acetylenic alcohols, ?,?-unsaturated aldehydes, and/or ?-alkenyl phenones, reduces or inhibits corrosion of metal equipment present during acidizing treatment in gas- or oilfield reservoirs with one or more acids. Also disclosed is a method for reducing or inhibiting corrosion of steel equipment present during an acid treatment of a gas- or oilfield reservoir with one or more acids by using a specific synthetic polymer as corrosion inhibitor in combination with an organic corrosion inhibiting compound having at least one unsaturated carbon-carbon bond, preferably selected from the group of acetylenic alcohols, ?,?-unsaturated aldehydes, and/or ?-alkenyl phenones.