Catalyst compositions which are particularly useful for the preparation of ethylene polymers having a narrow molecular weight distribution are obtained by (1) drying an inorganic oxide having surface hydroxyl groups, e.g., silica, alumina, magnesia, etc., to remove adsorbed water, (2) reacting the surface hydroxyl groups with at least a stoichiometric amount of an organometallic compound having at least one alkyl group attached to a Group III metal, e.g., a trialkylaluminum, (3) reacting the thus-treated inorganic oxide with a vanadium halide, such as (a) VOCl.sub.3, VOBr.sub.3, and/or mono-, di-, and/or trihydrocarbyloxy derivatives thereof and/or (b) VCl.sub.4, VBr.sub.4, and/or mono-, di-, tri-, and/or tetrahydrocarbyloxy derivatives thereof, and (4) reacting that reaction product with at least about 0.1 mol, per mol of organometallic compound, of an alcohol containing 1 to 18 carbon atoms.