A petroleum reservoir is a subsurface pool of hydrocarbons, primarily composed of oil and natural gas. These reservoirs are typically found in porous rock formations, where the hydrocarbons accumulate over time due to geological processes. The ability of the rock to store and transmit fluids is crucial for the reservoir's effectiveness in holding petroleum. Reservoirs are often located deep beneath the Earth's surface and can vary in size and shape. They are usually sealed by an impermeable layer of rock, known as a cap rock, which prevents the hydrocarbons from escaping. Understanding the characteristics of a petroleum reservoir is essential for successful oil exploration and production.