Sodium dodecyl (lauryl) sulfate (SLS)/water/decanol systems at a fixed water/SLS molar ratio of 144.0 (10 wt % SLS in water) and varying decanol/SLS molar ratios (Md) were studied through small-angle X-ray scattering (SAXS). Results from the distance and electron distribution functions retrieved from the SAXS curves show an increase in the maximum dimension of the spheroidal micelles with M-d ratios of up to 0.18. At M-d = 0.20, the micelle symmetries change from spherical to cylindrical, with an anisotropy (ratio between the longest and the shortest dimension) close to 1.8, according to bending energy requirements. Micellar aggregates self-assemble into cylinder-like particles with M-d ratios of up to 0.40, where a cylinder -> disk shape transformation is observed. The cylinder -> disk transition occurs at nearly the same Md as that of the nematic cylindrical -> nematic discotic liquid-crystalline phase transition in more concentrated systems. The transformation also agrees with bending energy requirements for the polar/apolar interface in mixed micelles. Furthermore, the amount of bound water per polar head remains the same in both the more diluted and the more concentrated systems.