It is now well established that the addition of the trivalent counterion, Al3+, induces surface multilayer formation in a range of anionic surfactants, including SLES, MES and SDS. A complex evolution in the extent of the surface ordering occurs with increasing surfactant and Al3+ concentration. In SDS / SLES mixtures some significant differences in that evolution of structure are observed compared to the pure components. These are attributed to the interplay with the associated bulk phase behaviour. In order to understand this potentially important trend SANS measurements are urgently required.