United States' oil production peaked in February 2020, at about 18,826,000 barrels per day. Control over supply Entities such as governments or cartels can reduce supply to the world market by limiting access to the supply through nationalizing oil, cutting back on production, limiting drilling rights, imposing taxes, etc. International sanctions, corruption, and military conflicts can also reduce supply. Nationalization of oil supplies Another factor affecting global oil supply is the nationalization of oil reserves by producing nations. The nationalization of oil occurs as countries begin to deprivatize oil production and withhold exports. Kate Dourian, Platts' Middle East editor, points out that while estimates of oil reserves may vary, politics have now entered the equation of oil supply. "Some countries are becoming off limits. Major oil companies operating in Venezuela find themselves in a difficult position because of the growing nationalization of that resource. These countries are now reluctant to share their reserves." According to consulting firm PFC Energy, only 7% of the world's estimated oil and gas reserves are in countries that allow companies like ExxonMobil free rein. Fully 65% are in the hands of state-owned companies such as Saudi Aramco, with the rest in countries such as Russia and Venezuela, where access by Western European and North American companies is difficult. The PFC study implies political factors are limiting capacity increases in Mexico, Venezuela, Iran, Iraq, Kuwait, and Russia. Saudi Arabia is also limiting capacity expansion, but because of a self-imposed cap, unlike the other countries. As a result of not having access to countries amenable to oil exploration, ExxonMobil is not making nearly the investment in finding new oil that it did in 1981. OPEC influence on supply OPEC is an alliance among 14 diverse oil-producing countries (as of January 2019: Algeria, Angola, Ecuador, Equatorial Guinea, Gabon, Iran, Iraq, Kuwait, Libya, Nigeria, Republic of the Congo, Saudi Arabia, United Arab Emirates, Venezuela) to manage the supply of oil. OPEC's power was consolidated in the 1960s and 1970s as various countries nationalized their oil holdings, and wrested decision-making away from the "Seven Sisters" (Anglo-Iranian, Socony, Royal Dutch Shell, Gulf, Esso, Texaco, Socal), and created their own oil companies to control the oil. OPEC often tries to influence prices by restricting production. It does this by allocating each member country a quota for production. Members agree to keep prices high by producing at lower levels than they otherwise would.