Biomass to energy conversion is an important action to reach sustainability, particularly on the small scale. Among different biomasses, however, vegetable oils can fire directly a compression ignited internal combustion engine with minimal pre-treatment of the fuel and adaptation of the engine. Energy production from waste cooking oils is even more interesting because it allows energy production while disposing of a residue. Data available in the Literature are rarely referring to commercially available engines therefore additional information is required on overall performance, emissions, and maintenance requirements. This paper presents the results of tests carried out by fuelling a commercially available 33 kW direct injection Diesel engine with different fuels, such as: Diesel (used as benchmark), biodiesel, linseed oil, RBDPO (Refined, Bleached and Deodorized Palm Oil), corn oil, soy oil, peanuts oil, sunflower oil, palm oil, waste frying sunflower oil and waste frying palm oil. Tests were performed at three different loads (10, 20, 30 kW) measuring fuel consumption, electricity production and exhaust gases temperature and composition. Fuel injectors were checked following each test to evaluate the fouling caused by different fuels. Results show that when increasing load fuel consumption shows a general decreasing trend while CO emissions decrease and NOx increase. All fuels show a higher consumption than diesel, due to a lower calorific value. Biodiesel CO emissions decrease with power increasing with a lower slope than diesel, therefore are lower at the lowest power and higher at the highest power. Biodiesel NO emissions are always 15-20% higher than diesel. Vegetable oil CO emissions are higher or lower than diesel ones depending on the power and on the fuel, while NO emissions are often higher than diesel ones. Specific fuel consumption, CO and NO emissions of waste frying vegetable oil are generally comparable to those of pure oils. (C) 2016 Elsevier Ltd. All rights reserved.