The majority of waste plastics today is either incinerated or buried for landfills. However, incineration of waste plastics can cause damages in furnace and air pollution problems. Shortage of available landfill sites also has become a serious concern. The methods of waste plastic recycling therefore have been paid much attention with the viewpoint of effective environmental protection. Liquefaction of waste plastics is an attractive recycling method in terms of producing fuel oil or chemicals. To date, most of the waste plastic liquefaction investigations have been limited to the areas not involving the use of a solvent. Pilot-scaled plants, such as those in the Fuji Recycle Process in Japan and the VCC Process in Germany, have been operated for some time. Although high conversion of waste plastics can be obtained at a temperature as low as 400{degrees}C, problems such as wide molecular weight distribution in the produced oil and high coking tendency have been encountered. Liquid-phase cracking of waste plastics has the potential of overcoming these problems, yet few research has been reported on the liquefaction behaviors for the liquid-phase cracking. Polyethylene (PE) has been regarded as one of the polymers difficult to liquefy, while the cracking of polystyrene (PS) ismore » considered to proceed in a way different from that of PE. Hence, we investigated the cracking of PS, PE, and their mixtures using solvents of different hydrogen donation capability. Differences in the liquefaction behaviors between PS and PE, influences of the solvent type, synergistic effects for the liquefaction of PS/PE mixtures, and a property in the oil are presented in this paper.« less