Abstract: A vanadium catalyst composition comprising:(i) the reaction product of a vanadium trihalide wherein the halogen is chlorine, bromine, or iodine, or mixtures thereof, and an electron donor, which is a liquid, organic Lewis base in which the vanadium trihalide is soluble;(ii) a silica support onto which component (i) is impregnated;(iii) a salt admixed with the silica support, the cation of said salt being selected from the group consisting of Groups I and II of the Periodic Chart of the Atoms;(iv) a halocarbon promoter; and(v) a hydrocarbyl aluminum cocatalyst.