A nodding donkey is the overground drive for a submersible pump in a borehole. A nodding donkey or horsehead pump is usually driven by an electric motor and 'nods' at a regular rhythm. Depending on the size of the submersible pump, it produces between 5-40 litres of petroleum-water mixture at each stroke. A 2-inch wide metal rod connects the head to the pump, located thousands of feet underground in the oil reservoir. This system is also commonly referred to as a beam pump, rod pump, grasshopper, pump jack, or jack pump. This type of arrangement is commonly used in onshore applications for relatively low-production wells.