According to the list of countries of the world sorted by their gross domestic product (GDP), These are the year 2007 figures, released by the World Bank.

1. United States
2. Japan
3. Germany
4. China
5. United Kingdom
6. France
7. Italy
8. Spain
9. Canada
10. Brazil
11. Russian
12. India
13. South Korea
14. Mexico
15. Australia

Saudi Arabia is the world’s leading petroleum exporter. Oil accounts for more than 90 percent of exports and nearly 75 percent of government revenues. Oil has provided Saudi Arabia with economic prosperity and a great deal of leverage in the international community.

Saudi Arabia’s economy is Petroleum-based; roughly 75% of budget revenues and 90% of export earnings come from the oil industry. The oil industry comprises about 45% of Saudi Arabia’s gross domestic product, compared with 40% from the private sector.

Saudi Arabia officially has about 260 billion barrels (4.1×1010 m³) of oil reserves, comprising about 24% of the world’s proven total petroleum reserves.

Reference - wiki -

With the gas prices reaching record levels there is renewed pressure on the U.S. government to bring windfall profits tax on oil companies.

In 1980, United States federal legislation was passed that levied such a tax on oil companies because of the profits they earned as a result of the sharp increase in oil prices brought about by the OPEC oil embargo.

This issue came to a head in 2005, when oil and gas companies, such as Exxon Mobil who reported profits of US$36 billion for the year, experienced unusually large profits due to rising energy prices.

What is windfall profits tax ?

According to investopedia
 A tax levied by governments against certain industries when economic conditions allow those industries to experience above-average profits.

Windfall taxes are primarily levied on the companies in the targeted industry that have benefited the most from the economic windfall, most often commodity-based businesses.

For ex: Oil

According to a USNEWS report If Exxon Mobil were a country, its 2007 profit would exceed the gross domestic product of nearly two thirds of the 183 nations in the World Bank’s economic rankings.

via [ USNEWS and investopedia ]