Alcohol based fuels attract the attention of alternative fuel researchers. Many studies have been performed about combustion, performance and emission characteristics of alcohol used in internal combustion engines. Fusel oil is an alcohol based fuel obtained as a by-product during alcohol fermentation. Up to the present there has been no study regarding the combustion characteristics of fusel oil in a spark ignition engine. In this experimental study, performance, emission and combustion characteristics of fusel oil were examined in a spark ignition engine at 2500 rpm and four different engine loads. In-cylinder pressures, heat release rates, flame development and flame propagation durations, crank angles corresponding 50% of total mass fraction burnt, engine torque, brake specific fuel consumptions, CO, HC and NOx emissions were investigated. The water content and lower heating value of the fusel oil aggravated the combustion. Flame development and flame propagation durations were prolonged. As a result engine performance dropped. In addition, fusel oil usage increased CO and HC emissions up to 21% and 25% respectively. NOx emissions decreased about 31% due to worse combustion performance of fusel oil. (C) 2015 Elsevier B.V. All rights reserved.