Oil reservoirs are natural underground formations that contain accumulations of crude oil and natural gas. These reservoirs are typically found in porous rock layers, where oil can flow through the spaces between the rock particles. The oil is trapped by impermeable rock layers above, preventing it from escaping to the surface. To extract oil from these reservoirs, companies drill wells to reach the oil deposits. The process involves various techniques, including primary recovery, which uses natural pressure, and secondary recovery, which injects water or gas to push more oil to the surface. Understanding oil reservoirs is crucial for efficient energy production.