This work investigates the performance and carbon dioxide (CO2) emissions from a stationary diesel engine fueled with diesel oil (B5) and hydrogen (H-2). The performance parameters investigated were specific fuel consumption, effective engine efficiency and volumetric efficiency. The engine was operated varying the nominal load from 0 kW to 40 kW, with diesel oil being directly injected in the combustion chamber. Hydrogen was injected in the intake manifold, substituting diesel oil in concentrations of 5%, 10%, 15% and 20% on energy basis, keeping the original settings of diesel oil injection. The results show that partial substitution of diesel oil by hydrogen at the test conditions does not affect significantly specific fuel consumption and effective engine efficiency, and decreases the volumetric efficiency by up to 6%. On the other hand the use of hydrogen reduced CO2 emissions by up to 12%, indicating that it can be applied to engines to reduce global warming effects. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.