Steam gasification of cellulose at high temperatures can yield synthesis gas in a process that stores and transports highly concentrated solar energy. We have characterized the composition of the product gas in the temperature range 1050-1600 K in opaque and transparent fluidized-bed reactors. Bed material was either a pure tabular alumina or a crushed platinum-on-alumina catalyst. In both cases, the carbon present in the cellulose feedstock was well converted to a gaseous product. However, in the tabular alumina bed, the product gas had the high hydrocarbon and low hydrogen content characteristic of a rapid or flash pyrolysis process.