A pump jack is a mechanical device used to extract oil from underground reservoirs. It operates by converting the rotary motion of a motor into a vertical motion, which lifts oil to the surface. The pump jack is commonly seen in oil fields and is often characterized by its distinctive "nodding" motion. These machines are essential in the oil extraction process, especially in areas where oil is not under sufficient pressure to flow naturally. The pump jack is connected to a subsurface pump that helps move the oil through the well and into storage tanks for further processing.