An olefin polymerization process is disclosed. The process comprises polymerizing olefins in the presence of a supported indenoindolyl catalyst system and an organoboron or organoaluminum-treated solid. The supported indenoindolyl catalyst system comprises a support, an organometallic complex comprising a Group 3 to 10 transition or lanthanide metal, M, and at least one indenoindolyl ligand that is &pgr;-bonded to M, and an activator. Performing the process in the presence of the organoboron or organoaluminum-treated solid surprisingly leads to an increased activity compared to polymerization processes performed without the treated solid.