In automotive engines which need oil for lubrication and other uses, an oil pump is required to keep oil flowing throughout the internal components. Some pumps are mechanical, while others are electronic.
Electric Oil Pumps
Some oil pumps are driven electronically. Many modern vehicles use them since they can send oil to the top of the engine before it is cranked over (which is why some owners manuals recommend waiting a few seconds after turning the key to the "on" position before starting the vehicle's engine).