The economy of Iran is a mixed and transition economy with a large public sector. It is the world's eighteenth largest by purchasing power parity (PPP). Some 60% of Iran's economy is centrally planned. It is dominated by oil and gas production, although over 40 industries are directly involved in the Tehran Stock Exchange, one of the best performing exchanges in the world over the past decade. With 10% of the world's proven oil reserves and 15% of its gas reserves, Iran is considered an "energy superpower."