Potential use of ultrahigh-resolution mass spectrometry for determination of sulfur-containing components of petroleum before and after ozonation has been described. The chemical composition of the petroleum before and after ozonation has been determined using a Fourier transform ion-cyclotron mass spectrometer with soft ionization techniques: atmospheric-pressure photoionization and positive-or negative-ion electrospray ionization. The article presents the main trends of change in the composition of petroleum sulfur components in the ozonation process as revealed on the basis of ultrahigh-resolution mass spectra.