The early oxidation stages of hydrogen-terminated single-crystalline (100) silicon exposed to a diluted N₂ : N₂O atmosphere at 850°C for different durations have been studied by x-ray photoemission spectroscopy, following the evolution of the Si 2p signal. Evidence is given that the usual analysis, in terms of five pairs of peaks attributed to silicon in the oxidation states from 0 to +4, does not account for the observed Si 2p signal. An explanation for silicon in unusual oxidation states is proposed.