AES and photoelectron spectra obtained with synchrotron radiation have been used to study the orientation dependence of oxygen adsorption on a cylindrically shaped Si single crystal. At 350 K for 2L exposures, the results revealed that the orientation dependence of the adsorption oxygen amount is comparatively weak, and it ean be understood in terms of step-enhanced adsorption. At intermediate exposures of ～10L, the penetration of oxygen atoms into the crystal lattice was found mainly on (111) orientation. This fact supports a "defect"-type model for the Si(lll)-(7×7) reconstruction.