High-resolution mass spectrometry enables molecular characterization of heavy petroleum fractions for petroleomics research. However, results from mass spectrometry are usually not quantitative. This paper provides strategies and solutions for obtaining quantitative analysis of a heavy petroleum fraction. The fluid catalytic cracking (FCC) slurry decant oil and its fractions were characterized by high-resolution Orbitrap mass spectrometry with various ionization techniques, such as positive- and negative-ion electrospray ionization, positive-ion atmospheric pressure photoionization, and chemical derivatizations. Molecular compositions obtained from various methods were combined and normalized using elemental composition of the FCC decant oil and its fractions. More than 7000 molecules of 20 class species were assigned and quantified. Aromatic hydrocarbon was the most abundant, accounting for 49.6 wt % of FCC decant oil. The non-basic N1O3 class species had a minimum content of 0.03 wt %. The concentration-assigned molecules ranged from 2.0 X 10(-3) to 2.1 x 10(4) wppm for C22H15N2 to C18H12, respectively.