The electronic structure of Co-doped anatase TiO(2) epitaxial thin films grown at different partial oxygen pressures is investigated using soft x-ray emission spectroscopy. The resonantly excited Co L(2,3) x-ray emission spectra of ferromagnetic Ti(0.96)Co(0.04)O(2) samples for the oxygen-deficient regime show that the ratio of integral intensities for Co L(2) and L(3) emission lines significantly decreases with respect to nonmagnetic samples in the oxygen-rich regime. This is due to L(2)L(3)M(4,5) Coster-Kronig transitions and suggests that ferromagnetic Ti(0.96)Co(0.04)O(2) samples have n-type charge carriers and Co-Co bonds between substitutional and interstitial Co atoms are present while Co-O bonds are dominant in nonmagnetic Ti(0.96)Co(0.04)O(2) samples in the oxygen-rich regime. Electronic structure calculations show that the presence of free charge carriers and Co segregation play a crucial role in strong ferromagnetism at room temperature in Co-doped TiO(2).