Algeria is a semi-presidential republic, with local constituencies consisting of 58 provinces and 1,541 communes. Algeria is a regional power in North Africa, and a middle power in global affairs. It has the highest Human Development Index of all non-island African countries and one of the largest economies on the continent, based largely on energy exports. Algeria has the world's sixteenth-largest oil reserves and the ninth-largest reserves of natural gas. Sonatrach, the national oil company, is the largest company in Africa, supplying large amounts of natural gas to Europe. Algeria's military is one of the largest in Africa, and has the largest defence budget on the continent. It is a member of the African Union, the Arab League, OPEC, the United Nations, and the Arab Maghreb Union, of which it is a founding member.