The thermal degradation of high-density polyethylene (HDPE) in decalin has been investigated as a method for the feedstock recycling of plastic wastes. The study is focused on the effects of the reaction time and temperature. The solvent increased the HDPE conversion and had a significant effect on the product distribution, which may be assigned mainly to the decalin participation on the reaction mechanism. Short reaction times and low temperatures in the presence of decalin contributed to an enhanced production of gaseous hydrocarbons. Longer reaction times and high temperatures in the presence of this solvent improved the production of C-5-C-55 hydrocarbons. The gaseous olefins and C-5-C-32 alpha-olefins increased with time and temperature; however, the best selectivity to olefins (96.5%) in the gaseous fraction was obtained at 5 h and 375 degrees C, whereas the higher selectivity to alpha-olefins (76%) within the C-5-C-32 fraction was achieved after 5 h and 425 degrees C.