Abstract: A fluidized-bed reactor for ammo-oxidation or oxidation and an ammo-oxidation or oxidation process using the reactor. The reactor comprises a vessel, a sparger for supplying and dispersing a gas containing an organic material, and a distributor for supplying and dispersing an oxygen-containing gas, the sparger comprising a header and a plurality of dispersion pipes connected laterally to the header, the dispersion pipes each having a plurality of orifices, wherein the hole size of an orifice farthest from the header is larger than the hole size of an orifice nearest the header, and the hole size of one orifice is larger than or equal to the hole size of adjacent orifice that is nearer the header than the one orifice.