Two-stage coprocessing of waste plastics with coal and petroleum resid was investigated using a one-third fractional factorial design. In the two-stage process, waste plastics were reacted in the first stage, and the liquid products from the first stage were then introduced into the second stage, which consisted of coal and petroleum resid. Four factors, each with three levels, were evaluated in the study, namely the catalyst type, the resid type, the plastic type, and the weight percent of coal. The catalysts were NiMo/Al2O3, NiMo/zeolite, and HZSM-5; the resids were Manji, Maya, and Hondo; the plastics were low-density polyethylene, mixed post-consumer, and mixed waste plastics collected in Germany; and the weight percents of coal were 0, 10, and 29%. The results from the factorial experiment were evaluated by determining their product distributions using solvent fractionation. The production of gas and hexane-soluble materials, as well as the conversion to THF-soluble materials, was measured. From the determination of the significance of each factor and factor interaction on the production of these products and the conversions obtained, the most effective conditions (i.e., the optimum factor level combination for the four factors) for performing two-stage coprocessing of coal, petroleum resid, and waste plastics using the factors studied were determined. The presence of coal, particularly at 29%, decreased the amount of conversion and production of hexane-soluble materials in the two-stage coprocessing reaction. By contrast, two-stage coprocessing of waste plastics and petroleum resid resulted in end products that were more conducive to further processing into chemical feedstocks and transportation fuels.