A novel melting gasifier (7) is disclosed, in which material at least largely comprising metal is melted in a fluidized bed. The latter is maintained by oxygen-containing gas laterally injected through approximately equidistant nozzles in the lower part of the melting gasifier. A carbon carrier and from above the material to be melted are also introduced into the melting gasifier. Over at least part of the fluidized bed height, the gasifier has a horizontal cross-section, which has different dimensions in two directions perpendicular to one another. The nozzles can project by different amounts into the gasifier vessel.