The discovery of Constrained Geometry Catalysts (CGC) for production of polyolefins allows one to make new polyolefins in a solution process. CGCs have a single active site for polymerization, and the bridged nature of the monocyclopentadienyl titanium complex allows facile incorporation of alpha olefins into random ethylene copolymers that are characterized by narrow molecular weight distributions and narrow comonomer distributions. In this paper, olefin copolymers (OCPs) of ethylene with propylene and octene comonomers produced with constrained geometry catalyst are described, and their behavior as viscosity index improvers in oil solutions is examined.A wide range of amorphous and semicrystalline OCPs have been produced and characterized. Crystallinity was measured by DSC, and molecular weights (Mw) were determined by GPC. Thickening efficiency and shear stability were measured as 1 wt% polymer solutions in oil, and the effects of Mw and crystallinity on these oil solution properties were analyzed by regression analysis. Several conventional OCPs also were compared as 1 wt% solutions with CGC polymers. Low temperature properties of oil solutions were studied as a function of polymer composition with a scanning Brookfield viscometer. For optimum performance, amorphous polymers must contain less than 1% crystallinity, and semicrystalline polymers must have crystallinity between about 10 and 16%. Results from GF-2 bench tests on fully formulated oils indicate that polymers made with CGC are suitable as VI improvers in engine oils.