A vacuum gas oil (VGO) and blends containing 5 and 10 wt % high density polyethylene, respectively, in the VGO were thermally and catalytically cracked in a fixed bed reactor at 510 degrees C and 20 h(-1) WHSV. The objective was to produce transportation fuels from direct cracking of polyethylene without prior pyrolysis at 450-500 degrees C as reported previously (Ng et al., 1993). Thermal cracking resulted in low overall conversion to gasoline and its secondary products including coke, although polyethylene in the blend was substantially converted. In contrast, high conversion was obtained from catalytic cracking. However, the gasoline yield of polyethylene depended on its concentration in the blend. At 5 wt % polyethylene, the gasoline produced from primary cracking appeared to be completely decomposed to gas and coke through secondary cracking whereas at 10 wt %, a substantial amount of gasoline was produced. Synergistic effect observed during catalytic cracking of the blends was discussed.