A process for producing petroleum products comprising: charging feedstock comprising mixed polymer materials into a reactor vessel of a reactor apparatus; applying heat energy to reactor vessel and converting feedstock to molten material while advancing the molten material through the reactor apparatus in an anaerobic operation; and controlling the energy input to the reactor vessel and controlling a temperature gradient within the reactor vessel to produce a petroleum gas product, wherein the free volume of the reactor vessel is at least 60% upon initial heating, wherein the reactor vessel does not rotate during the process, wherein the composition of the feedstock varies from about 10% to about 70% polyethylene, from about 10% to about 70% polypropylene, from about 10% to about 30% polystyrene and from about 0% to about 30% other commonly use polymeric materials such as polyvinyl chloride, polyester, polycarbonate, polymethyl methacrylate, nylon and the like, wherein the reactor apparatus comprises a plurality of sequential reactor zones along the horizontal axis of the reactor apparatus, and the molten material is advanced through the plurality of reactor zones as it is advanced through the reactor vessel of the reactor apparatus, wherein the feedstock and the products generated by the feedstock are conveyed along sequential reactor zones by means of agitation, wherein said agitation is provided by at least one helical screw, and wherein the energy input to the reactor apparatus is controlled by controlling the energy distribution within each of the plurality of the reactor zones to control cracking and recombination reactions generated by pyrolysis of the feedstock. charging feedstock comprising mixed polymer materials into a reactor vessel of a reactor apparatus; applying heat energy to reactor vessel and converting feedstock to molten material while advancing the molten material through the reactor apparatus in an anaerobic operation; and controlling the energy input to the reactor vessel and controlling a temperature gradient within the reactor vessel to produce a petroleum gas product, wherein the free volume of the reactor vessel is at least 60% upon initial heating, wherein the reactor vessel does not rotate during the process, wherein the composition of the feedstock varies from about 10% to about 70% polyethylene, from about 10% to about 70% polypropylene, from about 10% to about 30% polystyrene and from about 0% to about 30% other commonly use polymeric materials such as polyvinyl chloride, polyester, polycarbonate, polymethyl methacrylate, nylon and the like, wherein the reactor apparatus comprises a plurality of sequential reactor zones along the horizontal axis of the reactor apparatus, and the molten material is advanced through the plurality of reactor zones as it is advanced through the reactor vessel of the reactor apparatus, wherein the feedstock and the products generated by the feedstock are conveyed along sequential reactor zones by means of agitation, wherein said agitation is provided by at least one helical screw, and wherein the energy input to the reactor apparatus is controlled by controlling the energy distribution within each of the plurality of the reactor zones to control cracking and recombination reactions generated by pyrolysis of the feedstock.