High-resolution synchrotron radiation photoemission has been used to examine the oxidation states of Si atoms near the Si/SiO2 interface. The quality of the starting Si surfaces was intentionally varied and oxidation was done with pure O-2 and with a mixture of O-2 plus Cl-2. The distribution of intermediate oxidation states and the interface thickness was unaffected by Cl-2 exposure for atomically flat, well-ordered Si(100) or (111) surfaces. However, for disordered Si surfaces the presence of Cl-2 in the oxidizing gas reduced the concentration of Si1+ and Si2+ species by a factor of 2, indicating a tendency to produce better interfaces. In all cases, Cl was present near the SiO2/Si interface, bonded to Si, and in solution with SiO2 as Cl-2.