In this study, ab-initio density functional methods are used to examine the effects of nickel, copper, and chromium substitutions on unstable and intrinsic stacking fault energies in FCC iron. The aim of this study was to determine if these alloy additions favor the formation and stability of e-martensite. Nickel and copper additions are shown to increase intrinsic stacking fault energy whereas chromium is shown to have a parabolic relationship. Effects on the unstable stacking fault energy are also examined indicating chromium decreases the unstable stacking fault energy whereas Ni and Cu have a complex effect and are dependent upon proximity to the stacking fault.