This study investigated the engine performance and emissions of a supercharged engine fueled by hydrogen (H(2)), and three other hydrogen-containing gaseous fuels such as primary fuels, and diesel as pilot fuel in dual-fuel mode. The energy share of primary fuels was about 90% or more, and the rest of the energy was supplied by diesel fuel. The hydrogen-containing fuels tested in this study were 13.7% H(2)-content producer gas, 20% H(2)-content producer gas and 56.8% H(2)-content coke oven gas (COG). Experiments were carried out at a constant pilot injection pressure and pilot quantity for different fuel air equivalence ratios and at various injection timings. The experimental strategy was to optimize the pilot injection timing to maximize engine power at different fuel air equivalence ratios without knocking and within the limit of the maximum cylinder pressure. Better thermal efficiency was obtained with the increase in H(2) content in the fuels, and neat H(2) as a primary fuel produced the highest thermal efficiency. The fuel air equivalence ratio was decreased with the increase in H(2) content in the fuels to avoid knocking. Thus, neat H(2)-operation produced less maximum power than other fuels, because of much leaner operations. Two-stage combustion was obtained; this is an indicator of maximum power output conditions and a precursor of knocking combustion. The emissions of CO and HC with neat H(2)-operation were 98-99.9% and NOx about 85-90% less than other fuels. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.