Saudi Aramco, officially the Saudi Arabian Oil Company, most popularly known just as Aramco, is a Saudi Arabian national petroleum and natural gas company based in Dhahran. Saudi Aramco's value has been estimated at between US$1.25 trillion and US$10 trillion.Saudi Aramco has both the world's second largest proven crude oil reserves, at more than 260Goilbbl, and second largest daily oil production.Headquartered in Dhahran, Saudi Arabia, Saudi Aramco operates the world's largest single hydrocarbon network, the Master Gas System. Its 2013 crude oil production total was 3.4Goilbbl, and it manages over 100 oil and gas fields in Saudi Arabia, including 288.4 trillion standard cubic feet of natural gas reserves. Saudi Aramco operates the Ghawar Field, the world's largest onshore oil field, and the Safaniya Field, the world's largest offshore oil field.HistorySaudi Aramco's origins trace to the oil shortages of World War I and the exclusion of American companies from Mesopotamia by Great Britain and France under the San Remo Petroleum Agreement of 1920. The US Republican administration had popular support for an "Open Door policy", which Herbert Hoover, secretary of commerce, initiated in 1921. Standard Oil of California (SoCal) was among those US companies seeking new sources of oil from abroad.