Abstract: In the production of styrene, spontaneous polymerization of styrene monomer causes reduced efficiency and as such it is desirable to prevent the formation of polymer by the addition of inhibitors. A known inhibiting composition is 3,5-di-tert-butyl-4-hydroxy-N,N-dimethylbenzyl amine and carboxylic acid, or an anhydride of said carboxylic acid which is added to a styrene-containing mixture. However large quantities are required and often portions of the inhibiting composition are not utilized resulting in nonproductive loss. The efficiency of the specific inhibitor can be improved by supplying air simultaneously with the inhibiting composition in a weight ratio of 3,5-di-tert-butyl-4-hydroxy-N,N-dimethylbenzyl amine to carboxylic acid to air, said ratio being 1:1-0.05:0.05-15.