The co-pyrolysis of waste polyolefins [waste polyethylene (PE) and waste polypropylene (PP)] with waste motor oil (WMO) was performed at different ratios under a nitrogen atmosphere at 500 degrees C. The effects of WMO on the pyrolysis of waste polyolefins and their blends were investigated under identical conditions. The addition of WMO into waste polyolefins not only increased the liquid yields but also improved the properties of liquid products. In the most cases, the co-pyrolysis process had a positive synergistic effect on the liquid yields when compared with the calculated co-pyrolysis yields. The naphtha and paraffinic contents of the liquid products obtained from the co-pyrolysis of PE/WMO, PE/PP/WMO blends were higher than liquid products obtained from the pyrolysis of the individual waste polyolefins. The trace elements as well as heavy metals in the liquid products from the pyrolysis of WMO alone or the co-pyrolysis of waste polyolefins with WMO were observed to be lower than the WMO feed. The prominent gas products obtained from the pyrolysis of individual waste polyolefins and WMO or the co-pyrolysis of waste polyolefins/WMO blends were hydrocarbons and hydrogen. The heating values of the pyrolysis and co-pyrolysis gases were found to be in the range of 27.6-32.4 MJ Nm(-3). (C) 2016 Elsevier B.V. All rights reserved.