Abstract: Olefin catalyst systems comprising silica supports are provided. For example, in one embodiment, the olefin polymerization catalyst system comprises a silica support, a catalyst precursor compound, and an activator. The silica support comprises a plurality of silica gel particles. Each particle comprises a rigid network of amorphous silica. The particles are spherical, single gel particles that have an average aspect ratio of about 1.2 or less, an average pore volume of from about 1.4 ml/g to about 3 ml/g, an average surface area from about 200 m2/g to about 950 m2/g, and a median particle size from about 4 ?m to about 100 ?m.