Provided are ethylene-based copolymers, methods of preparing the same, lubricating oil compositions including the same, methods for preparing such lubricating oil compositions, and end uses for such ethylene-based copolymers and lubricating oil compositions. The ethylene-based copolymers may include from about 35 wt. % to about 60 wt. % of units derived from ethylene and at least 1.0 wt. % of one or more alpha-olefin comonomers having 3 to 20 carbon atoms. The ethylene-based copolymers are substantially amorphous and have a polydispersity index of about 2.8 or less.