Alternative gaseous fuels, like syn-gas and bio-gas, are attractive fuels for internal combustion engines due to energy and environmental concerns. Although the worldwide use of alternative gaseous fuels has increased, the knock properties of these fuels are not well understood. The methane number (MN) knock rating technique was selected based on its range and sensitivity. Eight alternative gaseous fuel compositions were simulated with a gas blending system and tested for MN in a Cooperative Fuel Research (CFR) F-2 engine. The alternative gaseous fuels ranged from 24 to 140 MN (natural gas typical range 75-95). (C) 2008 Elsevier Ltd. All rights reserved.