The economy of Qatar is one of the highest in the world based on GDP per capita, ranking generally among the top ten richest countries on world rankings for 2015 and 2016 data compiled by the World Bank, the United Nations, and the International Monetary Fund (IMF). The country's economy has grown despite sanctions by its neighbors, Saudi Arabia and the United Arab Emirates. Petroleum and natural gas are the cornerstones of Qatar's economy and account for more than 70% of total government revenue, more than 60% of gross domestic product, and roughly 85% of export earnings. Qatar has the world's third largest proven natural gas reserve and is the second-largest exporter of natural gas. Energy sector Before the emergence of petrol-based industry, Qatar was a poor pearl diving country. The exploration of oil and gas fields began in 1939. In 1973, oil production and revenues increased dramatically, moving Qatar out of the ranks of the world's poorest countries and providing it with one of the highest per capita incomes in the world. Qatar's economy was in a downturn from 1982 to 1989. OPEC (Organization of Petroleum Exporting Countries) quotas on crude oil production, the lower price for oil, and the generally unpromising outlook on international markets reduced oil earnings. In turn, the Qatari government's spending plans had to be cut to match lower income. The resulting recessionary local business climate caused many firms to lay off expatriate staff. With the economy recovering in the 1990s, expatriate populations, particularly from Egypt and South Asia, have grown again. Oil production will not long remain at peak levels of 500,000 barrels (80,000 m³) per day, as oil fields are projected to be mostly depleted by 2023. However, large natural gas reserves have been located off Qatar's northeast coast. These offshore gas fields also may contain significant oil and condensate reserves. For example, the state owned QatarEnergy corporation found two offshore oil fields in the 1960s. At the time production was too expensive. However, technological development led to production over 30 years later. The gas condensate can be refined to usual oil products in specialised refineries. The costs are a bit higher but it is normal today for companies to use the gas condensate too. Oil offshore production in 2008 for PS-2 and PS-3 blocks was about 31.1 million barrels (84,995 b/d). Joint Ventures facilities (PS-1, ALK, K & A): Combined oil production