A process for the preparation of higher olefins by oligomerization of ethylene, which comprises contacting ethylene with a catalyst in a solvent at temperatures ranging from -30* +80* C., the catalyst being prepared by the steps of reacting titanium tetrachloride with at least one ketone electron donor, and mixing the reaction product with an aluminum alkyl halide component containing 1.8 - 2.8 bonded halogen atoms per one aluminum atom.