In this work the composition of a hydrotreated distilled crude oil fraction (HTAL-FEED) and its heaviest steam cracking product fraction, the so-called pyrolysis fuel oil (HTAL-PFO), have been characterized in detail using high-temperature comprehensive two-dimensional gas chromatography (HT-GC x GC) coupled to a flame ionization detector (FID) and Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). Moreover, the HTAL-FEED and HTAL-PFO were characterized using elemental analysis and SARA fractionation to determine their bulk properties. Although the main compounds are saturates, the HTAL-FEED contains significant amounts of aromatic compounds, primarily mono- and di-aromatics but even up to penta-aromatics, which are responsible for the growth of large polycyclic aromatic hydrocarbons (PAH) formed during steam cracking that almost entirely make up the HTAL-PFO product. Quantitative results are obtained based on the HT GC x GC-FID chromatograms and the use of well-chosen internal standards, allowing similar to 90 wt% of the feedstock and similar to 60 wt% of HTAL-PFO to be quantified. FT-ICR MS analyses confirmed the presence of molecules heavier than penta-aromatics in the HTAL-FEED, as well as the very heavy character of HTAL-PFO consisting of highly condensed aromatic molecules with up to 16 fused aromatic rings. The analytical methodology can be applied to other steam cracking products, providing a near-molecular level insight into conversion and coke formation precursors during steam cracking of wide boiling range hydrocarbons.