Too often, major corrosion problems have been dealt with on the basis of galvanic or bimetallic reactions, not realizing that one of the major contributing factors was the presence of hydrogen sulfide. One of the areas where hydrogen sulfide has had its greatest impact is in the petroleum industry, primarily in the production of petroleum and its handling prior to the time that it arrives at a refinery. Another industry where hydrogen sulfide takes its toll is that of the collection and processing of sewage. Here not only does hydrogen sulfide react directly with metal, but it reacts indirectly and catastrophically with concrete as well. Sulfides can be a severe problem in marine corrosion. Micro organisms represented by sulfate reducing bacteria are commonly encountered in sea water. Coatings offer one of the few practical methods of corrosion control.