The emission characteristics of a spark ignition (SI) engine operated in turn on H-2 and some of its mixtures with CH4 and CO are examined experimentally. The role of changes in some key operating variables affecting the production of the pollutants CO, NOx and unburned hydrocarbons are examined and some guidelines for reducing the undesirable emissions are outlined. It is also shown that through determining the concentrations of CO and CO2 in the exhaust of a hydrogen fuelled engine, the lubricating oil consumption rates can be derived. The effects of changes in equivalence ratio, compression ratio and the onset of knock on oil consumption are described. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.