This work studies the chemistry of hexylbenzene pyrolysis under conditions of 450°C, 75 bar, and < 90 minutes residence time through kinetic modeling using Reaction Mechanism Generator (RMG) and experimentation using high pressure batch reactors analyzed by 2-dimensional gas chromatography with quadrupole mass spectrometry (GCxGC-qMS). The underlying motivation of this work is to understand alkylaromatic reactions in petroleum refining, and characterize the formation of two ring aromatics, likely precursors to coke. This work utilizes GCxGC-qMS to identify pyrolysis products that have two or more aromatic rings; these compounds are categorized into (I) bridged two ring aromatics, (II) fused two ring aromatics, and (III) compounds with more than two rings. Formation mechanisms of each of the categories are discussed, with supporting thermochemistry and kinetics from RMG’s database. Pathways discussed in this work can be extrapolated to higher molecular weight aromatics, bridging the understanding between the primary mechanism of alkylaromatic pyrolysis and coke formation.