Data on the content of oxygen-containing compounds as impurities in the feedstock of ethylene plant EP-300, the distribution of the impurities and compounds derived from them in the gaseous and liquid pyrolysis products, dilution steam condensate, water and hydrocarbon streams of the plant preparing pyrogas for compression, and in water streams of the dilution steam generation unit are cited. The influence of the oxygen-containing compounds on the water-chemical regime of the dilution steam generation unit is shown.