The industrial synthesis of higher olefins is generally performed via oligomerization of lower olefins by transition metal complexes or acidic catalysts. The broad variety of olefins that are nowadays produced by these reactions are used as polyethylene co-monomers or as intermediates in the synthesis of detergents, surface active compounds, lubricating oils, and plasticizers. Thus, in the Dimersol{reg_sign} process, butenes are dimerized into C{sub 8} olefins which are usually further hydroformylated giving C{sub 9} alcohols used in the manufacture of plasticizers. In spite of important research efforts devoted to these homogeneous phase oligomerization reactions, activity and conversion still need to be improved. In a more general sense, the separation of the products from the catalyst and the solvent is a major drawback, which leads to increased operational costs and environmental impact. Organochloroaluminate ionic liquids have been envisioned as solvents of nickel catalysts in oligomerization reactions to overcome this technical limitation. The solubility of nickel complexes and the poor solubility of olefins in polar and non-coordinating ionic liquids make possible the separation of the reaction products by simple decantation, with low costs and absence of by-products. In the present article, the authors report the use of 1-butyl-3-methylimidazolium chloro-ethyl-aluminate ionic liquids as solventsmore » in butene oligomerization catalyzed by nickel complexes in a two-phase system. 24 refs., 2 figs., 2 tabs.« less