The ordered structures formed in two experimental nickel base superalloys have been determined using selected area electron diffraction. Upon quenching from 1300 °C, the alloys contained ordered γ′ precipitates (L12 structure) and the matrix exhibited diffuse intensity at {1 1/2 0} positions, indicating the presence of short range order. The high refractory metal content of the alloys caused the D1a, DO22, and Pt2Mo prototype structures to form in the matrix following aging at 600, 700, and 800 °C. The detailed structural effects of the Ta and W quaternary additions are similar to those observed in Ni3(Mo, Al), Ni3(Mo,Ta), and Ni3(Mo, W) ternary alloys. The decomposition products observed in the quaternary alloys studied can be explained by considering the partitioning of solutes between the γ′ and the matrix.