Crude oil is a naturally occurring, unrefined petroleum product composed of hydrocarbon deposits and other organic materials. Crude oil can be refined to produce usable products such as gasoline, diesel and various forms of petrochemicals. It is a nonrenewable resource, also known as a fossil fuel, which means that it cant be replaced naturally at the rate we consume it and is therefore a limited resource.Crude oil is typically obtained through oil drilling, where it is usually found alongside other resources, such as natural gas (which is lighter, and therefore sits above the crude oil) and saline water (which is denser, and sinks below). It is then refined and processed into a variety of forms, such as gasoline, kerosene, and asphalt, and sold to consumers.Although it is often called black gold, crude oil has ranging viscosity and can vary in color to various shades of black and yellow depending on its hydrocarbon composition. Distillation, the process by which oil is heated and separated in different components, is the the first stage in refining.