Elemental compositions of components in feed and catalytically processed deasphalted oils were characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The processed oils which were hydrocracked over a zeolite catalyst at three different reaction temperatures (370,380, and 390 degrees C) were analyzed. Species of the deasphalted oils were ionized either by electrospray ionization (ESI) or by in-beam electron ionization (EI). The ESI mass spectra were obtained from every feed and processed deasphalted oil. Over 550 chemically different compounds were observed in the feed oil mass spectra. Molecular formulas for the detected peaks were calculated by using accurate mass. The compounds with one N atom as well as one N and S atoms were detected as major and minor component, respectively, in every mass spectrum. The number of the detected species in processed deasphalted oil decreases as the reaction temperature increases. However, the carbon distribution of NS-containing species shifts to high number as the reaction temperature increases. Molecular formulas distribution against Z-value (Z-value is defined as CnH2n+zNmSsOo) and C-number were investigated for the ESI mass spectra. Z-value distribution of the peaks assigned to N-compounds was convergent in its compounds with Z=-25 as increasing the reaction temperature. Detailed mass spectrum analysis reveals that compounds which were not detected in the feed oil were observed in the mass spectra of processed oils; N, S, and O-containing compounds. For the in-beam El only the processed oil at 390 degrees C yields approximately 700 resolved peaks at adopted probe temperature (300 degrees C) ofEI. Molecular formula analysis for the observed peaks was conducted as well as ESI. It reveals that the molecular formulas havingZ-value (-30 < Z < 2) and carbon number ranged from 8 to 31 except for (-18 < Z <-12,15 < C-number < 22) were contained in the processed deasphalied oil. Using complementary ionization techniques to characterize the feed and catalytic reacted deasphalted oils provide better understanding of fuel processing conditions. (c) 2007 Elsevier B.V. All rights reserved.