Saudi Arabia has an oil-based economy with strong government control over major economic activities. Saudi Arabia possesses 25% [3] of the world's proven petroleum reserves, ranks as the largest exporter of petroleum, and plays a leading role in OPEC. Saudi Arabia's economy is a centrally planned economy. Private enterprises do exist, they are however regulated by the Saudi government. The petroleum sector accounts for roughly 45% of budget revenues, 55% of GDP, and 90% of export earnings. About 40% of GDP comes from the private sector. Roughly five and a half million foreign workers play an important role in the Saudi economy, for example, in the oil and service sectors. The government is encouraging private sector growth to lessen the kingdom's dependence on oil and increase employment opportunities for the swelling Saudi population. The government has begun to permit private sector and foreign investor participation in the power generation and telecom sectors. As part of its effort to attract foreign investment and diversify the economy, Saudi Arabia acceded to the WTO in 2005 after many years of negotiations. With high oil revenues enabling the government to post large budget surpluses, Riyadh has been able to substantially boost spending on job training and education, infrastructure development, and government salaries.