Protective effects of aryloxycarbonylmethylisoquinolinium chlorides on the iron surface were studied. The best results were obtained with decylphenoxycarbonylmethylisoquinolinium chloride (DPCMIQC) containing the alkyl C 10 in the aryl fragment. This salt was used as an active component in an SNPKh-type corrosion inhibitor. Experimental data for this inhibitor were compared with the results obtained in bench and commercial field tests in West Siberia and the Ural-Volga region.