A high-density polyethylene was thermally cracked in both a closed tubing-bomb reactor at 450-500 degrees C and an open system using the same reactor at 480 degrees C. In the closed system, distillate yield increased at a higher temperature which also accelerated the formation of gases and coke. Secondary reactions such as saturation, isomerization, cyclization, and aromatization were found at high severity. In contrast, the open system produced less naphtha but more gas oil. Compositionally, the distillates contained more olefins, less saturates, and very little aromatics, compared with those from the closed system. Pyrolytic waxy products from polyethylene were catalytically cracked in a fixed-bed reactor at 470 and 510 degrees C, respectively. High yields of gasoline of improved quality and liquefied petroleum gas were obtained along with a small amount of low-value products such as dry gas, heavy cycle oil and coke.