Bitumen is a low-grade of crude oil which is composed of complex, heavy hydrocarbons. In an oil reservoir, bitumen is a thick, viscous fluid and must be extracted from the ground. When extracting it, a lot of heat and effort must be used to upgrade it to a better product. Although bitumen is hard to extract from the ground, it can bubble naturally to the surface of the Earth in petroleum seeps. These seeps are places where fossil fuels and petroleum products leak out of the Earth instead of being trapped deep below the ground. In these seeps, bitumen, asphalt, and tar bubble up into pools. Additionally, bitumen is the main fossil fuel component of oil sands. When bitumen combines with asphaltines a solid is formed that is useful for paving roads