A new reactor system was developed for recovery fuels from the waste plastic mixture in steam atmosphere. Firstly, the degradation mechanisms of eight kinds of plastics, two polyolefins (polyethylene and polypropylene), two polyamide resins (nylon-6 and nylon-6,6), polystyrene and three polyesters (polycarbonate, poly(butylene terephthalate) and poly(ethylene terephthalate), were investigated both in nitrogen and steam as the carrier gas. Plastics except for polyesters were degraded without any influences of the kinds of the carrier gas, leaving negligibly small amount of carbonaceous residue. Polyesters, which were degraded with producing large amount of the residue in nitrogen, were succeeded to be hydrolyzed at high reaction rates in steam with producing hardly the carbonaceous residue. Secondly, a mixture of the waste plastics was continuously degraded to produce heavy oil in steam atmosphere by using a new reactor system. This system was composed of three kinds of reactors connected in series. One was a reactor filled with stirred heat medium particles, which enabled the high heat transfer rate, the high holdup and the good contact of the melted plastics with steam. The second was a tank reactor. The last one was a fixed bed reactor with FeOOH catalyst particles, which showed the catalysis in steam for the decomposition both of a wax and sublimate materials generated by the degradation of plastics. Furthermore, the oil produced from the proposed reactor system was continuously upgraded to produce gasoline and kerosene over Ni-REY catalyst in steam atmosphere.