Coprocessing of common thermoplastics of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PBT) and acrylonitrile-butandiene-styrene (ABS) with waste lubricating oil was carried out. Statistical pentagonal design experiments in a microreactor system (40 ml capacity) were done to find out the optimum conditions for cracking of the plastic/waste oil mixtures into oils. From these experiments, it was shown that the oil yields of common thermoplastics such as PE, PP and PS reached nearly complete conversion under their respective optimum pyrolytic conditions suggesting the ease of thermal cracking of each polymer into oils. Meanwhile, both PET as a condensation polymer and ABS as a graft copolymer gave relatively lower yields in oil compared to the afore mentioned common thermoplastics.