Modern power generation systems can produce clean, economical energy. Gas turbines, modem reciprocating engines and fuel cells may all play a role in new power production, both for electric power and mechanical drive applications. Compared to their counterparts of even a decade ago, new power systems have significantly reduced pollutant emissions. However, the careful balance between low emissions and operating performance often requires that system performance be optimized on a single fuel. Thus, for example, a gas turbine designed to produce low emissions on natural gas may not easily achieve the same emission goals on a different gaseous fuel. This paper reviews the various issues associated with changes in gaseous fuel composition for low-emission turbines, reciprocating engines and fuel cells. (C) 2001 Published by Elsevier Science Ltd.