The shifts of the (111) and (200) x‐ray diffraction lines have been measured by both the centroid and the peak method. From these measurements the stacking fault probability &agr; and the twinning fault probability &bgr; can be obtained on powdered samples prepared by filing. These results show a parabolic type of dependence of &agr; with composition, whereas the stacking fault probability &agr; obtained from previous measurements using the same technique on Cu‐Zn and Ag‐Cd alloys had a linear dependence with composition.By means of a simple argument the relative stacking fault energies for these alloys can be deduced and compared with those obtained on similar Cu‐Ge alloys by Howie using thin‐film electron microscopy and by Haasen and King using tensile tests.