Addition reactions have been proposed as a significant pathway for coke formation in the liquid-phase cracking of heavy oils and bitumens. In order to study the kinetics of olefin addition in the liquid phase, two alkyl-bridged aromatic compounds, with molecular weights of 899.70 g/mol and 1127.99 g/mol, were thermally cracked with 1-hexadecene, 1-octadecene, or trans-stilbene, in a batch microreactor at 375−430°C for 15 to 45 min. Reaction products were analyzed by gas chromatography, high-performance liquid chromatography, matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), and proton nuclear magnetic resonance ( 1 H NMR) spectroscopy. Kinetic data indicate a first-order reaction in model compound concentration, with energetics consistent with a free-radical chain mechanism. Tandem MS/MS and 1 H NMR spectra of the products are consistent with olefin addition through the alkyl bridge of the bridged aromatics. The results imply that (i) the addition products are able to abstract hydrogen to give detectable products faster than they decompose, and (ii) the addition products can react even more readily than the parent compounds.