Significant interest exists in the deployment of 13Cr martensitic stainless steels in offshore oil and gas projects. Several grades of 13Cr exist, with the seemingly negligible variations between their chemistries and fabrication processes. The different grades perform dramatically differently, especially regarding cracking resistance in sour or chloride-containing environments. Determination of the proper 13Cr grade for sour service involves the investigation of domain diagrams, and often requires further fitness-for-service testing. However, the validity of each domain diagram for only one chloride concentration or content greatly limits their practicality for selecting 13Cr, thus impeding the ability to determining if fitness-for-service testing should be performed and its potential outcome.