Increased hydrotreating severity resulted in decreased tri-ring + molecules and increased smaller molecules (e.g., naphthalenes, indanes, benzenes) and hydrogenated species of these smaller molecules (e.g., tetralins, decalins, saturated cyclics). Use of the pilot-scale laboratory coker provides sufficient quantities of distillate liquids so as to provide distillable product from co-coking reactions. Product distributions obtained from the co-coking experiments were found to be very similar to an industrial coker product, in terms of gas, liquid and solid products. Vacuum distillation of the collected overhead liquid from co-coking experiments was performed to provide gasoline, jet fuel, diesel, and fuel oil products. The boiling point distributions and chemical compositions in the co-coking experiments were found to be relatively dependent on hydrotreatment levels of decant oil. An increase in saturated cyclics, tetralins and decalins, but a decrease in paraffins, benzenes, and naphthalenes in the co-coking experiments, was measured by GC/MS as the hydrotreatment severity increased. No tri-ring + compounds were identified in jet fuel fraction.