Abstract: The method of forming a catalytic component for use in the polymerization of ethylene or a copolymer of ethylene and a C.sub.3 to C.sub.12 alpha olefin in a gas-phase comprising impregnating a porous metal oxide support with at least one titanium compound, magnesium compound, and chlorine compound, and prepolymerizing ethylene or a copolymer of ethylene and a C.sub.3 to C.sub.12 alpha olefin, a least partially in suspension, in the presence of said porous metal oxide support and at least one alkylaluminum compound until a degree of prepolymerization is reached which is suitable for the subsequent gas-phase of fluidized bed polymerization, and the method of polymerizing olefins utilizing the catalysts formed by the prepolymerization.