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. Therefore, an empirical model compiled from fitness-for-service data and supported by oilfield experience led to the development of a resource tool designed to provide quick validation of fitness-for-service test results, increasing the efficiency of decision-making for 13Cr selections. Also, this paper summarizes the pros and cons of different 13Cr OCTG alloys, in regards to the mechanical strengths and performances in sour/non-sour conditions, high chloride levels, low pH values and presence of CO2. Specifically noted are the H2S partial pressures in excess of NACE MR 0175 limits where 13Cr materials can be successfully utilized.