Recently, sewage sludge has particularly become an important problem all over the world because of its harmful impacts on the environment and living beings. It should be converted to combustible gas or useful energy in order to remove all its negative effects and to contribute to a significant portion of the power generation. In this study, combustible gas production from sewage sludge was experimentally investigated using a gasification technique by a downdraft gasifier. The amount of combustible gases, which are H-2, CO, CH4, C2H2 and C2H6, was found to be 19-23% of the total produced gases in the operating conditions. The average calorific value of the product gas was obtained between 2.55 and 3.2 MJ (N m(3))(-1). However, its average energy quantity was estimated between 12.19 and 28.97 MJ h(-1). Consequently, combustible gases were produced from sewage sludge by utilizing as a feedstock in a downdraft gasifier. Henceforth, sewage sludge can be considered a renewable energy source for gasifiers in order to produce thermal energy to help get rid of sewerage all over the world. (C) 2000 Elsevier Science Ltd. All rights reserved.