Process for preparing olefins, which comprises the following steps: a) preparation of a synthesis gas comprising carbon monoxide and hydrogen, b) introduction of carbon dioxide recirculated from step d) into the synthesis gas during or after the preparation of synthesis gas as per step a), c) conversion of the synthesis gas having a hydrogen to carbon monoxide ratio of ≦1.2:1 which is obtained in step b) into olefins in the presence of a Fischer-Tropsch catalyst, d) removal of the carbon dioxide comprised in the reaction product from step c), where the ratio of hydrogen to carbon monoxide in step c) is set via step b).