Abstract: An installation for gasifying coal in a fluidized bed under high pressure has a vessel resistant to the high pressure and a reactor disposed in the interior of the vessel and having a principal chamber constituting a gasification chamber which permits the establishment of a principal fluidized bed of substantial depth and an auxiliary fluidized bed of a smaller depth. An inclined traveling grate forms the bottom of the gasification chamber and has a lower grate portion supporting the principal fluidized bed and an upper grate portion supporting the auxiliary bed situated in a space between the vessel walls and the gasification chamber. The principal and auxiliary fluidized beds are maintained in hydrostatic equilibrium.