The present invention relates to a process to make light olefins, in a combined XTO-OC process, from an oxygen-containing, halogenide-containing or sulphur-containing organic feedstock comprising: a0) providing a first portion and a second portion of said oxygen-containing, halogenide-containing or sulphur-containing organic feedstock, a) providing a catalyst comprising zeolitic molecular sieves containing at least 10 membered ring pore openings or larger in their microporous structure, b) providing an XTO reaction zone, an OC reaction zone and a catalyst regeneration zone, said catalyst circulating in the three zones, such that at least a portion of the regenerated catalyst is passed to the OC reaction zone, at least a portion of the catalyst in the OC reaction zone is passed to the XTO reaction zone and at least a portion of the catalyst in the XTO reaction zone is passed to the regeneration zone; c) contacting the first portion of said oxygen-containing, halogenide-containing or sulphur-containing organic feedstock in the XTO reactor with the catalyst at conditions effective to convert at least a portion of the feedstock to form a XTO reactor effluent comprising light olefins and a heavy hydrocarbon fraction; d) separating said light olefins from said heavy hydrocarbon fraction; e) contacting said heavy hydrocarbon fraction and the second portion of said oxygen-containing, halogenide-containing or sulphur-containing organic feedstock in the OC reactor with the catalyst at conditions effective to convert at least a portion of said heavy hydrocarbon fraction and oxygen-containing, halogenide-containing or sulphur-containing organic feedstock to light olefins.