Saudi Arabia, officially known as the Kingdom of Saudi Arabia, is the largest Arab state in Western Asia by land area (approximately 2,250,000 km2), and the second-largest in the Arab world after Algeria. The Kingdom was founded in 1932 and the governance system is based on constitutional monarchy. Its population is estimated at 31.4 million, of which 33% are registered expatriates. The per capita income of Saudi Arabia is US$ 55,125 (US$ at PPP) for 2016 (IMF). Saudi Arabia was ranked 38 out of 188 in the latest edition of UNDP’s Human Development Report (2016). The life expectancy at birth is estimated at 74.1 years while the mean schooling is estimated at 7.8 years (HDR 2016). Saudi Arabia has the world's largest oil reserves which are concentrated largely in the Eastern Province. It has also the world's sixth largest natural gas resources.