X-ray photoelectron spectroscopy (XPS) was used to investigate changes in nitrogen.functionalities present in Chinese Huadian (HD), Maoming (MM) and Yaojie (YJ) oil shales during pyrolysis. Throughout the process (T <= 600 degrees C), most of the nitrogen contained in raw oil shale samples was retained in their semi-cokes. Five peaks of nitrogen functionalities (N 1s) appeared in the XPS spectra of raw HD, MM and YJ oil shale samples and their semi-cokes: N-6 (pyridine), N-A (amino), N-5 (pyridone), N-Q (quaternary nitrogen) and N-XI (pyridine N-oxide). To obtain an acceptable fit, an additional peak at 404 (+/- 0.5) eV (N-X2) was required in the N 1s spectra of the samples. N-5 could either represent pyridone or a mixture of pyridone and pyrrolic nitrogen forms, the most abundant ones in all samples. At a relatively low temperature (300 degrees C) the desorption reaction occurred and the amount of chemisorbed oxygen associated nitrogen (N-X2) decreased significantly. As the pyrolysis temperature increased,from 300 to 500 degrees C, pyridine N-oxide was converted to pyridone, and, simultaneously, the latter was converted to pyridine and pyridine structures associated with oxygen quaternary nitrogen. In the semi-cokes of Huadian and Maoming oil shale samples at 600 degrees C, most of the pyridone was converted into pyridine and quaternary nitrogen. At this temperature, especially the condensation reaction of pyridine into quaternary nitrogen occurred in the semi-coke of Yaojie oil shale sample, while quaternary nitrogen represented the nitrogen atoms in the interior of precursors of the graphene layers.