In order to cope with power shortage in rural areas of developing countries and to reduce greenhouse gas emissions, we study the performance of small biogas-fueled internal combustion engines of which power is less than 5 kW. In particular, the influence of compression ratio on the engine is primarily examined. By decreasing the combustion chamber volume (from 19.3 cc to 16.6 cc), compression ratio (from 8.01:1 to 9.22:1) is increased to enhance brake power output (from 2.2 kW to 2.68 kW), brake thermal efficiency (from 22.0% to 29.8%) and brake specific fuel consumption of the engine (from 290.6 (sic) to 218.6 (sic)). In addition, as means to examine the effect of the biogas composition on engine performances, various carbon dioxide dilution ratios (from 0% to 50%) are tested. At lowest carbon dioxide dilution, maximum engine performance is obtained. (C) 2017 Elsevier Ltd. All rights reserved.