It is notoriously known that localized corrosion in sour fields is a challenge persisting in the oil and gas industry since it has frequently been seen as a cause for catastrophic failures of upstream pipelines. Hence prediction and mitigation of H2S localized corrosion of mild steel is of key importance for integrity management. However our current understanding of H2S localized corrosion from literature or experience is far from being conclusive with respect to mechanisms of H2S localized corrosion. Although numerous experimental studies of H2S corrosion of mild steel have been completed in the laboratory environmental conditions leading to H2S localized corrosion are unclear and the causes of H2S localized corrosion are uncertain. Therefore seeking an experimental condition in the laboratory that can replicate localized corrosion in a sour environment is critical to understand mechanisms of localized corrosion. The focus of the present research was to explore environmental conditions for probable H2S localized corrosion mechanism(s). When severe localized corrosion was observed in experiments there was an indication of the formation of greigite and/or pyrite. Based on those experimental results a hypothesis for H2S localized corrosion was proposed and tested with respect to possible galvanic effects (due to a difference in electrical conductivity associated with polymorphous iron sulfides).