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:a) providing a catalyst comprising zeolitic molecular sieves containing 10 member and larger channels 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 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 in the OC reactor with the catalyst at conditions effective to convert at least a portion of said heavy hydrocarbon fraction to light olefins.