mixtures thereof methylalumoxanes are preferred the amount of alumoxane is adjusted to provide an aluminum to group 4 metal al m molar ratio within the range of about 20 to about 2000 a more preferred ratio is within the range of about 50 to about 500 most preferred is the ratio from about 150 to about 250 the alumoxane can be combined with the treated support before see example a or after the complex is combined with the support alternatively the alumoxane and complex can be premixed prior to combination with the support see example b a solution of the metallocene complex with or without the alumoxane is conveniently combined with the treated silica and solvents are removed in vacuo to recover a silica supported metallocene that is useful in the olefin polymerization process of the invention the supported catalyst typically contains from about 0 001 to about 0 5 mmol more preferably from about 0 01 to about 0 05 mmol of transition metal per gram of catalyst triisobutylaluminum tibal is used as a scavenger the amount of tibal used is within the range of about 10 to about 1000 moles per mole of group 4 transition metal a more preferred range is from about 20 to about 500 moles per mole of group 4 metal i surprisingly found that tibal works exceptionally well when compared with other common scavengers particularly triethylaluminum teal compare the results in table 1 below tibal provides an unexpected 50 increase in activity compared with teal the process of the invention can be used in any olefin polymerization that uses a supported catalyst preferably the.