Lubricating oil compositions are provided which contain bimodal copolymer compositions, and in particular bimodal ethylene-α-olefin copolymer compositions. The copolymer compositions comprise first and second ethylene-α-olefin copolymer components. The bimodal compositions are particularly useful as viscosity or rheology modifiers, e.g., in lubricating oil compositions. Lubricating oil compositions comprising the copolymer compositions advantageously exhibit enhanced shear stability index (SSI) and thickening efficiency (TE) values, while maintaining excellent low-temperature properties such as pour point, mini-rotary viscometer viscosity, and cold crank simulation performance.