This work describes the development of a procedure for the preferential oxidation of nitrogen compounds of a gas oil sample from Brazilian petroleum. The sample was first submitted to an extraction procedure, based on preparative liquid ion-exchange chromatography (IEC), to characterize the main nitrogen compounds. The instrumental analysis was performed by gas chromatography with a mass spectrometer detector (GC/MSD), and the compounds were identified using the GC/MSD library (Wiley). The IEC analysis shows that the nitrogen compounds were concentrated mainly in the acid and neutral fractions of the sample. The hindrance influence of the nonbonded electron pair of the N atom in the IEC process was studied with a standard mixture of three nitrogen compounds. The oxidation reaction used was efficient for the preferential oxidation of nitrogen compounds while keeping the distribution of the other class compounds of the gas oil unchanged. Experiments for the reaction scale reduction were also performed.