Coking and co-coking of decant oil and decant oil/coal blends were studied using a large laboratory-scale delayed coker. Four different coals were used in this study: Powelton/Eagle, Canterberry, Pittsburgh, and Marfork. Two petroleum-based decant oils were used for delayed coking and co-coking purposes. In the co-coking experiments, the coal was reacted at 20 and 30% by weight in the blend. Coker pressure was adjusted to two different values for evaluation. Co-coking of decant oil/coal blends produced higher amounts of coke than coking of decant oil alone. Product distribution ranges for co-coking were found to be 22-39% coke, 50-71% liquid, and 1-16% gas. Increasing the amount of coal in the blend and coker back-pressure resulted in a higher percentage of coke formation (which resulted in coke of lower quality), while the total liquid product yield decreased. The objective of this study was to determine molecular contributions from coal to the overhead liquid. The isolated overhead liquid products were subsequently vacuum-distilled into typical refinery boiling range materials (gasoline, jet fuel, diesel and fuel oil). Vacuum distillates were further characterized using GC/MS to investigate the effect of particular coals on the liquid produced from co-coking. GC/MS analyses demonstrated that vacuum fractions of co-coking overhead liquid had higher quantity aromatic components than those of coking. On the other hand, vacuum distillation results showed that co-coking of coal with a decant oil at a higher coal percentage (30 wt% versus 20 wt%) in the blend increased the lighter boiling range materials (i.e., gasoline, jet fuel, diesel) in the overhead liquid. In addition, it was found that higher coker back-pressure (50 psig versus 25 psig) also increased the lighter boiling range materials in the overhead liquid.