The invention relates to a catalyst system, containing at least one metallocene, at least one co-catalyst, at least one supporting material and optionally additional organometallic compounds. The catalyst system can be used advantageously for polymerising olefins, as it obviates the use of aluminoxanes, such as methylaluminoxane (MAO), which is conventionally used in excess quantities as a co-catalyst, whilst at the same time producing strong catalyst activity and excellent polymer morphology.