Formation of iron sulfide is recognized as a key step in formation of fouling in petroleum processing. Iron may be naturally present or generated by corrosion of pipes and process equipment by naphthenic acids. Limited data and analyses are available to quantify the effects of corrosion products on the propensity and threshold fouling conditions. Based on the experimental investigation and the literature data, an investigative analysis is performed to understand the underlying mechanisms of iron sulfide induced fouling/coking in upgrading processes.