This disclosure relates to a method and an apparatus for the delivery of a multi-component olefin polymerization catalyst to a polymerization reactor. The components soluble in a first solvent are delivered under pressure along with that solvent in a first delivery conduit. The components that are insoluble in the first solvent but are soluble in a second solvent are delivered under pressure in a second delivery conduit which is arranged coaxially with and disposed within the first conduit, such that the inner conduit and outer conduit terminate at a common catalyst component mixing conduit which extends into the polymerization reactor and in which the catalyst components mix to form an active polymerization catalyst.