As a new corrosion resistant alloy (CRA) high strength 15Cr martensitic stainless steel (0.03C-15Cr-6Ni-2Mo-1Cu) offers an OCTG material for the completion of HTHP deepwater wells and large bore gas wells due to a combination of high specified minimum yield strength (SMYS) of 125 ksi without cold drawing good notch toughness and superior CO2 corrosion resistance. However the service limits of 15Cr steel in oil and gas production well environments containing H2S are not clear due to the complex interaction of environmental factors such as chloride concentration pH H2S partial pressure and temperature. This paper describes an experimental study of the resistance of 15Cr steel to environmentally assisted cracking including sulfide stress cracking and stress corrosion cracking in simulated sour oil and gas well environments. Three heats of 15Cr steel material were selected as representative of the maximum values of strength/hardness and minimum alloy content per the alloy specification. 15Cr steel is evaluated using NACE tensile specimens stressed at 90% of actual yield strength in acetic acid/acetate and CO2/bicarbonate buffered solutions containing 10000 and 100000 mg/L chloride at 75°F 200°F and 400°F. The limits of use of the 15Cr steel in sour well environments are presented and discussed in detail.