Petroleum crude oil is the main energy source for making transportation fuel, providing about 90% of the US gasoline and most of the diesel and jet fuel. It comes in many different varieties, with different densities and sulfur contents. Worldwide there are about 100 million barrels consumed each day, with the United States accounting for 20% of this consumption. Crude oil is supported by an immense infrastructure, which will make it difficult for another energy type to displace it as a transportation fuel. Using the United States as an example, there are about 135 refineries with an operating capacity of nearly 19 million barrels per day. To deliver oil to these refineries there are about 55,000 miles of pipelines, and to deliver products from the refinery to the approximately 150,000 filling stations there are another 95,000 miles of pipelines. Because of this infrastructure, gasoline and diesel are widely available for use in vehicles of all sizes.