A large number of high-density polyethylene (HDPE) po cc der samples produced by Phillips technology were taken from an industrial polymerization reactor and their catalyst residue content was determined by X-ray fluorescence spectroscopy. The chemical structure of the powder was characterized by diffuse reflectance infrared spectroscopy (DRIFT), while the functional group content of samples processed in the presence and absence of a phenolic antioxidant was determined by Fourier transform infrared spectroscopy (FTIR). The melt flow index (MFI) of all processed samples was measured. Oxygen induction time (OIT) measurements were carried out to characterize the oxidative stability of 15 selected stabilized samples. The results indicate that the distribution of both the amount of chromium-based catalyst residues and their composition are very heterogeneous in the produced polymer. With increasing catalyst residue content, the concentration of double bonds increases in the samples extruded with or without stabilizer. Viscosity was not influenced by catalyst residues, while discoloration increased slightly with increasing catalyst residue content. The stability of the processed polymer also depends on the concentration of double bonds and on other factors. Since other components of the catalyst, including the SiO2 support, also take part in the reactions occurring during processing, chromium content is not the sole, and perhaps not even the decisive, factor determining the properties and especially the stability of HDPE produced by a Phillips catalyst.