Question: When did the country with the largest economy in Africa become a member of OPEC?

full_context: Document 1: Nigeria: Nigeria is often referred to as the ``Giant of Africa '', owing to its large population and economy. With 186 million inhabitants, Nigeria is the most populous country in Africa and the seventh most populous country in the world. Nigeria has the third - largest youth population in the world, after India and China, with more than 90 million of its population under age 18. The country is viewed as a multinational state as it is inhabited by over 500 ethnic groups, of which the three largest are the Hausa, Igbo and Yoruba; these ethnic groups speak over 500 different languages and are identified with a wide variety of cultures. The official language is English. Nigeria is divided roughly in half between Christians, who live mostly in the southern part of the country, and Muslims, who live mostly in the north. A minority of the population practise religions indigenous to Nigeria, such as those native to the Igbo and Yoruba ethnicities.
Document 2: List of African countries by GDP (PPP): Region Rank Country 2015 GDP (PPP) millions of International dollars -- Africa 5,736,700 Nigeria 1,192.00 Egypt 995.97 South Africa 724.01 Algeria 570.64 Morocco 274.53 6 Angola 185.25 7 Sudan 167.42 8 Ethiopia 159.22 9 Tanzania 150.4 10 Kenya 143.05 11 Tunisia 127.21 12 Ghana 113.35 13 Libya 92.88 14 Uganda 79.75 15 Ivory Coast 78.34 16 Cameroon 72.11 17 Zambia 64.65 18 Democratic Republic of the Congo 63.27 19 Botswana 37.16 20 Senegal 36.30 21 Madagascar 35.56 22 Gabon 34.41 23 Chad 33.73 24 Mozambique 32.00 25 Burkina Faso 31.18 26 Mali 29.15 27 Zimbabwe 28.90 28 Republic of the Congo 27.92 29 Equatorial Guinea 25.94 30 Mauritius 24.84 31 Namibia 24.51 32 Benin 21.16 33 Malawi 20.56 34 Rwanda 20.32 35 Niger 18.96 36 Mauritania 16.43 37 Guinea 15.28 38 Swaziland 10.87 39 Togo 10.82 40 Eritrea 7.94 41 Burundi 7.88 42 Somalia 5.90 43 Lesotho 5.78 44 Gambia 3.27 45 Liberia 3.78 46 Cape Verde 3.48 47 Djibouti 3.09 48 Seychelles 2.53 49 Guinea - Bissau 1.94 50 Central African Republic 1.62 51 Comoros 1.21 52 São Tomé and Príncipe 0.66
Document 3: OPEC: Country Region Membership Years Population (2016 est.) Area (km) Oil Production (bbl / day, 2016) Proven Reserves (bbl, 2016) Algeria North Africa 1969 -- 40,606,052 2,381,740 1,348,361 12,200,000,000 Angola Southern Africa 2007 -- 28,813,463 1,246,700 1,769,615 8,423,000,000 Ecuador South America 1973 -- 1992, 2007 -- 16,385,068 283,560 548,421 8,273,000,000 Equatorial Guinea Central Africa 2017 -- 1,221,490 28,051 227,000 1,100,000,000 Gabon Central Africa 1975 -- 1995, 2016 -- 1,979,786 267,667 210,820 2,000,000,000 Iran Middle East 1960 -- 80,277,428 1,648,000 3,990,956 157,530,000,000 Iraq Middle East 1960 -- 37,202,572 437,072 4,451,516 143,069,000,000 Kuwait Middle East 1960 -- 4,052,584 17,820 2,923,825 101,500,000,000 Libya North Africa 1962 -- 6,293,253 1,759,540 384,686 48,363,000,000 Nigeria West Africa 1971 -- 185,989,640 923,768 1,999,885 37,070,000,000 Qatar Middle East 1961 -- 2,569,804 11,437 1,522,902 25,244,000,000 Saudi Arabia Middle East 1960 -- 32,275,687 2,149,690 10,460,710 266,578,000,000 United Arab Emirates Middle East 1967 -- 9,269,612 83,600 3,106,077 97,800,000,000 Venezuela South America 1960 -- 31,568,179 912,050 2,276,967 299,953,000,000 OPEC Total 478,498,000 12,150,695 35,221,740 1,209,103,000,000 World Total 7,618,511,000 510,072,000 80,622,287 1,650,585,000,000 OPEC Percent 6% 2% 44% 73%
Document 4: OPEC: Country Region Membership Years Population (2016 est.) Area (km) Oil Production (bbl / day, 2016) Proven Reserves (bbl, 2016) Algeria North Africa 1969 -- 40,606,052 2,381,740 1,348,361 12,200,000,000 Angola Southern Africa 2007 -- 28,813,463 1,246,700 1,769,615 8,423,000,000 Ecuador Americas 1973 -- 1992, 2007 -- 16,385,068 283,560 548,421 8,273,000,000 Equatorial Guinea Western Africa 2017 -- 1,221,490 28,051 227,000 1,100,000,000 Gabon Western Africa 1975 -- 1995, 2016 -- 1,979,786 267,667 210,820 2,000,000,000 Iran Middle East 1960 -- 80,277,428 1,648,000 3,990,956 157,530,000,000 Iraq Middle East 1960 -- 37,202,572 437,072 4,451,516 143,069,000,000 Kuwait Middle East 1960 -- 4,052,584 17,820 2,923,825 101,500,000,000 Libya North Africa 1962 -- 6,293,253 1,759,540 384,686 48,363,000,000 Nigeria Western Africa 1971 -- 185,989,640 923,768 1,999,885 37,070,000,000 Qatar Middle East 1961 -- 2,569,804 11,437 1,522,902 25,244,000,000 Saudi Arabia Middle East 1960 -- 32,275,687 2,149,690 10,460,710 266,578,000,000 United Arab Emirates Middle East 1967 -- 9,269,612 83,600 3,106,077 97,800,000,000 Venezuela Americas 1960 -- 31,568,179 912,050 2,276,967 299,953,000,000 OPEC Total 478,498,000 12,150,695 35,221,740 1,209,103,000,000 World Total 7,588,065,000 510,072,000 80,622,287 1,650,585,000,000 OPEC Percent 6% 2% 44% 73%
Document 5: Nigeria: As of 2015[update], Nigeria is the world's 20th largest economy, worth more than $500 billion and $1 trillion in terms of nominal GDP and purchasing power parity respectively. It overtook South Africa to become Africa's largest economy in 2014. Also, the debt-to-GDP ratio is only 11 percent, which is 8 percent below the 2012 ratio. Nigeria is considered to be an emerging market by the World Bank; It has been identified as a regional power on the African continent, a middle power in international affairs, and has also been identified as an emerging global power. Nigeria is a member of the MINT group of countries, which are widely seen as the globe's next "BRIC-like" economies. It is also listed among the "Next Eleven" economies set to become among the biggest in the world. Nigeria is a founding member of the Commonwealth of Nations, the African Union, OPEC, and the United Nations amongst other international organisations.
Document 6: Oil reserves in Saudi Arabia: The proven oil reserves in Saudi Arabia are the 2nd largest in the world, estimated to be (Gbbl hereafter), including 2.5 Gbbl in the Saudi–Kuwaiti neutral zone. They are predominantly found in the Eastern Province. These reserves were the largest in the world until Venezuela announced they had increased their proven reserves to 297 Gbbl in January 2011. The Saudi reserves are about one-fifth of the world's total conventional oil reserves, a large fraction of these reserves comes from a small number of very large oil fields, and past production amounts to 40% of the stated reserves.
Document 7: OPEC: Organization of the Petroleum Exporting Countries (OPEC, / ˈoʊpɛk / OH - pek, or OPEP in several other languages) is an intergovernmental organization of 14 nations as of May 2017, founded in 1960 in Baghdad by the first five members (Iran, Iraq, Kuwait, Saudi Arabia, Venezuela), and headquartered since 1965 in Vienna. As of 2016, the 14 countries accounted for an estimated 44 percent of global oil production and 73 percent of the world's ``proven ''oil reserves, giving OPEC a major influence on global oil prices that were previously determined by American - dominated multinational oil companies.
Document 8: OPEC: OPEC's stated mission is ``to coordinate and unify the petroleum policies of its member countries and ensure the stabilization of oil markets, in order to secure an efficient, economic and regular supply of petroleum to consumers, a steady income to producers, and a fair return on capital for those investing in the petroleum industry. ''The organization is also a significant provider of information about the international oil market. As of May 2017, OPEC's members are Algeria, Angola, Ecuador, Equatorial Guinea, Gabon, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia (the de facto leader), United Arab Emirates, and Venezuela, while Indonesia is a former member. Two - thirds of OPEC's oil production and reserves are in its six Middle Eastern countries that surround the oil - rich Persian Gulf.
Document 9: Oil reserves: Based on data from OPEC at the beginning of 2013 the highest proved oil reserves including non-conventional oil deposits are in Venezuela (20% of global reserves), Saudi Arabia (18% of global reserves), Canada (13% of global reserves), and Iran (9%).
Document 10: Nigeria: Nigeria is often referred to as the "Giant of Africa", owing to its large population and economy. With approximately 182 million inhabitants, Nigeria is the most populous country in Africa and the seventh most populous country in the world. Nigeria has one of the largest populations of youth in the world. The country is viewed as a multinational state, as it is inhabited by over 500 ethnic groups, of which the three largest are the Hausa, Igbo and Yoruba; these ethnic groups speak over 500 different languages, and are identified with wide variety of cultures. The official language is English. Nigeria is divided roughly in half between Christians, who live mostly in the southern part of the country, and Muslims in the northern part. A minority of the population practise religions indigenous to Nigeria, such as those native to Igbo and Yoruba peoples.
Document 11: List of African countries by GDP (nominal): 2017 Rank Country Nominal GDP ($billions) Nominal GDP per capita (US $) Notes Nigeria 376.284 1,994.235 South Africa 349.299 6,179.870 Egypt 237.037 2,500.772 Algeria 178.287 4,292.272 Angola 124.209 4,407.657 6 Sudan 119.00 1,428.000 7 Morocco 109.824 3,151.145 8 Ethiopia 80.874 872.840 9 Kenya 79.511 1,701.550 10 Tanzania 51.725 1,033.567 11 Ghana 47.032 1,663.190 12 Democratic Republic of the Congo 41.441 478.237 13 Ivory Coast 40.360 1,616.981 14 Tunisia 40.275 3,496.286 15 Cameroon 34.006 1,400.743 16 Libya 31.331 4,858.672 17 Uganda 26.349 699.410 18 Zambia 25.504 1,479.542 19 Zimbabwe 17.491 1,175.723 20 Botswana 17.168 7,876.997 21 Senegal 16.463 1,038.094 22 Mali 15.318 810.771 23 Gabon 15.206 7,971.589 24 Namibia 12.687 5,413.508 25 Mozambique 12.681 429.296 26 Burkina Faso 12.569 663.806 27 Mauritius 12.428 9,794.102 28 Madagascar 11.463 447.558 29 Equatorial Guinea 10.725 12,726.956 30 Chad 9.872 810.163 31 Guinea 9.721 749.463 32 Benin 9.238 830.404 33 Rwanda 9.137 771.702 34 Congo 8.513 1,958.174 35 Niger 8.253 439.997 36 Somalia 7.382 547.32 37 Malawi 6.206 323.740 38 Eritrea 5.813 979.692 39 Mauritania 5.116 1,317.938 40 Togo 4.767 611.133 41 Swaziland 4.491 3,914.821 42 Sierra Leone 3.641 491.448 43 Burundi 3.396 312.463 44 Liberia 3.285 729.292 45 South Sudan 2.870 228.034 46 Lesotho 2.768 1,425.310 47 Djibouti 2.029 1,988.765 48 Central African Republic 1.928 386.806 49 Cape Verde 1.741 3,237.597 50 Seychelles 1.482 15,685.955 51 Guinea - Bissau 1.350 794.107 52 The Gambia 1.009 480.040 53 Comoros 0.652 787.831 54 São Tomé and Príncipe 0.379 1,785.280 -- Total 2,191.104
Document 12: Nigeria: Nigeria was ranked 30th in the world in terms of GDP (PPP) in 2012. Nigeria is the United States' largest trading partner in sub-Saharan Africa and supplies a fifth of its oil (11% of oil imports). It has the seventh-largest trade surplus with the US of any country worldwide. Nigeria is the 50th-largest export market for US goods and the 14th-largest exporter of goods to the US. The United States is the country's largest foreign investor. The International Monetary Fund (IMF) projected economic growth of 9% in 2008 and 8.3% in 2009. The IMF further projects an 8% growth in the Nigerian economy in 2011.
Document 13: Oil reserves in Saudi Arabia: The proven oil reserves in Saudi Arabia are the second largest in the world, estimated to be 268 billion barrels (43 × 10 ^ m) (Gbbl hereafter), including 2.5 Gbbl in the Saudi -- Kuwaiti neutral zone. They are predominantly found in the Eastern Province. These reserves were the largest in the world until Venezuela announced they had increased their proven reserves to 297 Gbbl in January 2011. The Saudi reserves are about one - fifth of the world's total conventional oil reserves, a large fraction of these reserves comes from a small number of very large oil fields, and past production amounts to 40% of the stated reserves.
Document 14: Nigeria: According to the International Organization for Migration, Nigeria witnessed a dramatic increase in remittances sent home from overseas Nigerians, going from USD 2.3 billion in 2004 to 17.9 billion in 2007. The United States accounts for the largest portion of official remittances, followed by the United Kingdom, Italy, Canada, Spain and France. On the African continent, Egypt, Equatorial Guinea, Chad, Libya and South Africa are important source countries of remittance flows to Nigeria, while China is the biggest remittance-sending country in Asia.
Document 15: Japan: Japan is a member of the ASEAN Plus mechanism, UN, the OECD, the G7, the G8, and the G20, and is considered a great power. Its economy is the world's third-largest by nominal GDP and the fourth-largest by purchasing power parity. It is also the world's fourth-largest exporter and fourth-largest importer.
ground_truth: 1971
sub_queries: What is the largest economy in Africa? Answer: Nigeria
when did Nigeria become a member of opec Answer: 1971