The US Gulf Coast has a large concentration of refineries designed to process very heavy crude oil. At present, the refineries are dependent on heavy crude from Venezuela, including crude from Venezuela's own massive Orinoco oil sands. The United States is the number one buyer of crude oil exported from Venezuela. The large trade relationship between the US and Venezuela has persisted despite political tensions between the two countries. However, the volume of oil imported into the US from Venezuela dropped in half from 2007 to 2014, as overall Venezuelan exports have dropped, and also as Venezuela seeks to become less dependent on US purchases of its crude oil. The Keystone pipeline is seen as a way to replace imports of heavy oil-sand crude from Venezuela with more reliable Canadian heavy oil.