In the present study, microwave plasma gasification of two kinds of coal and one kind of charcoal was performed with various O-2/fuel ratios of 0-0.544. Plasma-forming gases used under 5 kW microwave plasma power were steam and air. The changes in the syngas composition and gasification efficiency in relation to the location of the coal supply to the reactor were also compared. As the O-2/fuel ratio was increased, the H-2 and CH4 contents in the syngas decreased, and CO and CO2 increased. When steam plasma was used to gasify the fuel with the O-2/fuel ratio being zero, it was possible to produce syngas with a high content of hydrogen in excess of 60% with an H-2/CO ratio greater than 3. Depending on the O-2/fuel ratio, the composition of the syngas varied widely, and the H-2/CO ratio necessary for using the syngas to produce synthetic fuel could be adjusted by changing the O-2/fuel ratio alone. Carbon conversion increased as the O-2/fuel ratio was increased, and cold gas efficiency was maximized when the O-2/fuel ratio was 0.272. Charcoal with high carbon and fixed carbon content had a lower carbon conversion and cold gas efficiency than the coals used in this study. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.