In early 2017, Qatar's total population was 2.6 million: 313,000 Qatari citizens and 2.3 million expatriates. Islam is the official religion of Qatar. In terms of income, the country has the third-highest GDP (PPP) per capita in the world, and the sixth-highest GNI per capita (Atlas method). Qatar is classified by the UN as a country of very high human development, having the third-highest HDI in the Arab world after United Arab Emirates and Saudi Arabia. Qatar is a World Bank high-income economy, backed by the world's third-largest natural gas reserves and oil reserves.