Oil reservoirs are natural underground formations that contain accumulations of crude oil. These reservoirs are typically found in porous rock layers, where oil can flow and be extracted. The oil is often trapped by impermeable rock layers above, which prevent it from escaping to the surface. The formation of oil reservoirs occurs over millions of years, as organic materials, such as dead plants and animals, are buried and subjected to heat and pressure. This process transforms the organic matter into oil, which can then migrate through the rock layers until it becomes trapped in a reservoir. Understanding these formations is crucial for the oil industry and energy production.