Process for the preparation of an olefin polymer using metallocenes containing specifically substituted indenyl ligands A highly effective catalyst system for the polymerization of olefins comprises a cocatalyst, preferably an aluminoxane, and a metallocene of the formula I in which, preferably M1 is Zr or Hf, R1 and R2 are alkyl or halogen, R5 is hydrogen or alkyl, R3 and R4 are alkyl, where R3, R4 and R5 may be halogenated, —(CR7R8)m—R6—(CR7R8)n— is a single- or multi-membered chain in which R6 may also be a (substituted) heteroatom, and m+n is zero or 1.