Compression ignition engines have proved to be the best option in heavy duty applications like transportation and power generation, but rapid depleting sources of conventional fossil fuels, their rising prices and ever increasing environmental issues are the major concerns. The present study deals with performance and emission analysis of blends of waste plastic oil obtained by catalytic pyrolysis of waste high-density polyethylene with diesel in a CI engine with varying loads. The experimental results show that the brake thermal efficiencies at all load conditions are lower as compared to that of diesel fuel, exhaust gas temperature increases with increase in engine load. The BSFC increases with increase in WPO blend ratio and decreases with increase in engine load. Mechanical efficiency increases with increasing brake power for all fuel blends. The NOx emission and CO emission increase with increase in percentage of waste plastic oil in blends, NOx emission decreases while CO emission increases with increase in engine load. The unburnt hydrocarbon emission decreases with increase in the engine load and increases with increase in percentage of waste plastic oil in blends. The carbon dioxide emission for the blends is lower than diesel for almost all loads and all blends. (C) 2013 Elsevier Ltd. All rights reserved.