The objective of this study was to estimate the heating value and investigate combustion characteristics of densified refuse derived fuel (RDF-5) produced from oil sludge. There were four main components in the RDF-5 tested. They were PE (polyethylene), wood powder, coal powder and oil sludge. We used calorimeter to have all components and RDF-5 tested for their heating values. The heating value of RDF-5 was found to be the simple weighted average of the heating value of each component. To study combustion characteristics, we performed experiments to measure the ignition and extinction time of each RDF-5 with different compositions. The results showed that the ignition characteristics had a strong relation with the oil sludge content. When the mass ratio of oil sludge is increased, the RDF becomes harder to burn and has a lower burning mass loss rate; meanwhile, the no ignition line resides at lower position, i.e. higher temperature. We also measured the relation between temperature and mass loss fraction associated with the burning and heating of different RDF-5 compositions. It was found that the burning of wood powder as an ingredient is faster than that of coal powder. The experimental results improved the understanding of the application of RDF-5 and demonstrated the combustion characteristics of RDF-5 based on oil sludge. (C) 2013 Elsevier Ltd. All rights reserved.