Mixtures of different polyolefins may be made by direct, preferably simultaneous, polymerization of one or more polymerizable olefins using two or more transition metal containing active polymerization catalyst systems, at least one of which contains cobalt or iron complexed with selected ligands. The polyolefin products may have polymers that vary in molecular weight, molecular weight distribution, crystallinity, or other factors, and are useful as molding resins and for films.