Concerns over the depletion of fossil fuels and global warming have increased the need for alternative-renewable energy sources. Biomass is one of the renewable and nonconventional energy sources and it also includes municipal solid wastes and animal wastes. Concentrated animal feeding operations produce large quantity of dairy biomass which might result in land and water pollution if left untreated. Different methods are employed to extract the available energy from the dairy biomass which includes co-firing and gasification. Earlier studies on gasification of dairy manure with different steam fuel ratios resulted in increased production of hydrogen. However, the gas mixture has low heat value due to large amount of diluent nitrogen. In order to enhance gas heat values, dairy biomass was gasified in a medium with enriched oxygen varying from 24% to 28% oxygen on volume basis. The effect of enriched air mixture, equivalence ratio and steam fuel ratio on the performance of fixed bed gasifier was studied. Limited studies were done using a mixture of carbon dioxide and oxygen as the gasification medium in order to explore the possibility of complete separation of CO2 and increase the heating value of gas mixture. The results show that the peak temperature and carbon dioxide production increases with corresponding decrease in carbon monoxide with increase in oxygen concentration in the incoming gasification medium. Higher heating value (HHV) of the gases decreases with increase in equivalence ratio (decrease in oxygen concentration). The gases produced using carbon dioxide and oxygen mixture had a higher HHV when compared to that of air and enriched air gasification. (C) 2011 Elsevier Ltd. All rights reserved.