Co-pyrolysis of high density polyethylene with low cost additives, such as bituminous coal, bagasse fly ash, coal-based thermal power plant fly ash, and deoiled cake of jatropha, has been carried out in a batch reactor in the presence of nitrogen at 450 degrees C under atmospheric pressure. Liquid products obtained by co-pyrolysis were characterized by ASTM D86 and gas chromatography/mass spectrometry. The yield of liquid product was found to be 54% upon pyrolysis of only high density polyethylene. It increased to between 63 and 80% when high density polyethylene was co-processed with bagasse fly ash, coal-based thermal power plant fly ash, bituminous coal, and deoiled cake of jatropha. ASTM D86 (boiling point distribution) analyses of liquid product from only high density polyethylene pyrolysis indicated that 62% diesel-like, 35% gasoline-like, and 3% heavier had formed. Co-processing high density polyethylene with bagasse fly ash, coal-based thermal power plant fly ash, bituminous coal, and deoiled cake of jatropha considerably (by 16 to 30%) improved the gasoline-like fraction's yield. This improvement was observed in the order of bagasse fly ash > coal-based thermal power plant fly ash > bituminous coal > deoiled cake of jatropha > high density polyethylene, while the yield of the diesel-like fraction followed the reverse order. Gas chromatography/mass spectrometry analyses demonstrated that the co-processing afforded 45-55% increase in C-6-C-12 fractions over that from high density polyethylene only. This increase paralleled the trend observed for gasoline-like fractions. Co-processing led to the addition of aromatics (2%) and oxygenates (6-15%) at the cost of paraffins (reduction by about 10-20%) in the liquid products. In general, results indicated that there exists a synergy of reactive species when high density polyethylene was co-processed with bagasse fly ash, coal-based thermal power plant fly ash, bituminous coal, and deoiled cake of jatropha.