The electronic structure of the CuO2 planes and CuO3 chains in single domain crystals of YBa2Cu3Ox has been investigated as a function of oxygen concentration (6≤×≤7) using polarization-dependent x-ray absorption spectroscopy at the O1s and Cu2p core absorption edges. The polarization-dependent observation of unoccupied states with O2p and with Cu3d orbital character parallel to the crystallographic a, b, and c axes of the crystals allows the determination of hole states near the Fermi level in Cu3dx2−y2 and O2px,y orbitals in the planes and in Cu3dy2−z2 and O2py,z orbitals in the chains. The onset of superconductivity does not significantly change the hole occupation.