The invention relates to a process for preparing linear α-olefins, wherein ethylene 1a is conducted into the oligomerization reactor 2 in the liquid phase. The oligomerization reactor 2 has a mechanical stirrer 2a in order to ensure optimal mixing of the liquid ethylene and of the catalyst in the liquid phase. From the top of the oligomerization reactor 2, vaporized ethylene is drawn off together with light α-olefins and a small proportion of the organic solvent. The gas mixture drawn off from the top of the reactor 2 is condensed together with gaseous fresh ethylene 7 by means of heat exchanger 3 and separator 4. The liquid phase drawn off from the separator 4 is conducted by means of circulation pump 5a as liquid ethylene input 1a back into the oligomerization reactor 2. The liquid products of the oligomerization reaction are drawn off 8 laterally from the base of the reactor 2.