The pyrolysis of polyolefins (low-density and high-density polyethylene and polypropylene) in a new kind of reactor, a conical spouted bed, has been studied in the 450-600 degreesC range and the kinetics of the formation of wax and individual gaseous products and significant groups of components have been determined. The activation energy of wax formation is similar for both polyethylenes (214 kJ mol(-1) for that of low density and 225 kJ mol(-1) for that of high density) and lower for polypropylene (176 M mol(-1)). The characteristic gas-solid contact of this reactor is especially suitable for selectively obtaining wax (92 wt % from polypropylene and 80 wt 176 from both polyethylenes) due to the high gas linear-velocity. Wax composition determined by Fourier transform infrared spectrophotometry indicates that it is a less branched and that its olefinic content is higher than that of commercial waxes.