Gasification of five Greek lignites of various origins was investigated in an isothermal fluidised bed pilot reactor at 750-900°C and 1-10 bar. After initial, cold-model fluidisation tests, carbon dioxide, steam, argon and carbon monoxide were used as gasifying media in varying compositions, in order to determine the role of each component in lignite reactivity and product distribution. Rapid conversion of C, H and O was achieved, with no detectable mass transport limitations. Carbon monoxide inhibited reaction at partial pressures above 0.3 bar. In the presence of steam, carbon dioxide gasification was 3-4 orders of magnitude slower and reaction proceeded predominantly via steam gasification. Based on these results, the gasifier requirements of such a process were evaluated.