Processes for preparing aluminoxane comprising: bringing into contact under reaction conditions in an inert atmosphere a liquid containing reaction mixture comprising: (i) a water in oil emulsion comprising water and at least one emulsifier in a first hydrocarbon solvent; and (ii) an organoaluminum compound capable of forming aluminoxane in a second hydrocarbon solvent; provided that the aluminoxane produced by the reaction is present in solution under the reaction conditions. In a preferred embodiment a support carrier for the aluminoxane: (i) is present during the contact step or (ii) is introduced following contact. A polymerization catalyst can be prepared wherein the support carrier is SiO2 and a Group 3 to Group 10 metal containing single site complex is mixed with the aluminoxane. Catalysts suitable for polymerizing an olefin such as ethylene or copolymerizing an olefin with at least one C3 to C20 alpha-olefin can be produced.