In this paper we discuss the influence of sodium dodecyl sulfate (SDS) and l-octanol on the phase behavior of(water/NaCl)-decane-sodium bis(2-ethylhexyl) sulfosuccinate (AOT) microemulsion systems. The two additives were chosen to mimic the effect of surface-active impurities such as the hydrolysis products of AOT, often present in commercial AOT samples or forming in AOT microemulsions. The investigation was carried out to clarify some contrariety of AOT phase diagrams published and to explain the origin of an isolated two-phase island, which so far represented a widely accepted peculiarity of the AOT system.