The present book explores the experimental production of liquid hydrocarbons by thermo-catalytic degradation of waste high-density polyethylene using kaolin clay, and sodium bentonite as catalysts at lab scale. The types of liquid fuel have been produced by using mutated catalysts. The experimental results show that mutated kaolin clay and sodium bentonite clay have prominent characteristics in the conversion of waste polymers into useful hydrocarbons. Optimal studies explore that the maximum liquid fuel yield is caused by the mixture of acid-treated catalysts. 61.89% of oil yield has been increased with acid-treated catalysts whereas 38.07% of increased oil yield has been calculated with base-treated catalysts. Without using any catalysts thermal degradation of waste high-density polyethylene is recommended for the production of gaseous products. Maximum gas yield has been calculated without using a catalyst.