With the late 20th century discovery of the bitumen deposits of the Orinoco Petroleum Belt, Venezuela is home to two major oil producing regions and more than 200 billion barrels of proven oil reserves. After decades of development, the wells of the Maracaibo region, which produce a medium grade crude, are declining in importance. The Orinoco basin has only begun to be tapped, however, and holds significant potential. Although plentiful, Orinoco crude is extra heavy (highly viscous) and sour (laden with a variety of contaminants, including sulfur). In some cases, the oil must be superheated to be extracted from the ground. After that, it cannot be put directly into a pipeline; usually it must be "upgraded," or stripped of contaminants, before it can be efficiently transported.