Iran is an energy superpower and the petroleum industry in Iran plays an important part in it. In 2004, Iran produced 5.1 percent of the world's total crude oil ( per day), which generated revenues of US$25 billion to US$30 billion and was the country's primary source of foreign currency. At 2006 levels of production, oil proceeds represented about 18.7% of gross domestic product (GDP). However, the importance of the hydrocarbon sector to Iran's economy has been far greater. The oil and gas industry has been the engine of economic growth, directly affecting public development projects, the government's annual budget, and most foreign exchange sources. In FY 2009, the sector accounted for 60% of total government revenues and 80% of the total annual value of both exports and foreign currency earnings. Oil and gas revenues are affected by the value of crude oil on the international market. It has been estimated that at the Organization of the Petroleum Exporting Countries (OPEC) quota level (December 2004), a one-dollar change in the price of crude oil on the international market would alter Iran's oil revenues by US$1 billion. In 2012, Iran, which exported around 1.5 million barrels of crude oil a day, was the second-largest exporter among the Organization of Petroleum Exporting Countries. In the same year, officials in Iran estimated that Iran's annual oil and gas revenues could reach $250 billion by 2015. However, the industry was disrupted by an international embargo from July 2012 through January 2016. Iran plans to invest a total of $500 billion in the oil sector before 2025. History The era of international control, 1901–1979 The history of Iran's oil industry began in 1901, when British speculator William D'Arcy received a concession from Iran to explore and develop southern Iran's oil resources. The exploration in Iran was led by George Reynolds. The discovery of oil on May 26, 1908 led to the formation in 1909 of the London-based Anglo-Persian Oil Company (APOC). By purchasing a majority of the company's shares in 1914, the British government gained direct control of the Iranian oil industry, which it would not relinquish for 37 years. After 1935 the APOC was called the Anglo-Iranian Oil Company (AIOC). A 60-year agreement signed in 1933 established a flat payment to Iran of four British pounds for every ton of crude oil exported and denied Iran any right to control oil exports. In 1950