Recent regulatory sharp curbs on coal power plants have compelled industries to adopt alternative sources of fuels. Biomass/fossil fuel co-gasification could be a pathway through more sustainable energy production technologies. As a basis for co-gasification study, the characteristics of single-fuel switchgrass and coal steam gasification in an atmospheric pilot scale bubbling fluidized bed reactor were studied. Increasing the steam-to-fuel ratio at 860 degrees C caused a moderate increase in the Hy and CO2 concentrations and decreases in the CO and CH4 concentrations, due to more steam-CH4 reforming and water-gasification reaction of CO. With increasing reactor temperature, the Hy concentration increased, whereas the CO, CH4, and CO2 concentrations fell slightly. Fall switchgrass gasification resulted in higher carbon, hydrogen and cold gas efficiencies than spring harvest gasification, possibly due to higher potassium concentration and hence, greater reactivity of the fall switchgrass. The equilibrium model was unable to predict the syngas composition properly. Adding an extra methanator stoichiometric reactor to produce methane based on the empirical CH4 concentration, and removing part of the carbon, hydrogen and steam before introducing the feed and gas agent streams to the reactor based on experimental carbon, hydrogen, and steam efficiencies, the kinetically modified model predicted the syngas composition accurately. (C) 2014 Elsevier Ltd. All rights reserved.