Steel normally corrodes quite uniformly in sulfide solutions with the formation of a black iron sulfide corrosion product. However, severe pitting has been known to occur in sour oil field brines. In order to shed some light on conditions required for pitting, a laboratory study was undertaken in which a potential-time technique and a duplex cell were used. The potential-time technique revealed that steel having a black oxide surface (mill scale) pitted in the presence of chlorides. In addition, the pitting potential was found to be independent of pH between 3 and 6 where the greatest pitting was observed. Observations made with the duplex cell suggest that the anolyte need not be of low pH for pitting to occur.