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The Ferdows, Mound, and Zageh Fields

Location: The Persian Gulf, off the coast of southern Iran

Estimated Reserves: 38 billion barrels

Details: Discovered in 2003, these three interconnected fields are among the largest oil deposits ever found. Ferdows is the largest, with 30.6 billion barrels. This figure may seem astounding, but its usually not possible to extract all the oil from a field due to technological and financial constraints. Plus, assessing how much oil these deposits can actually yield will take more drilling. If these fields can be largely exploited, though, they will be a huge boon to OPEC at a time when other oil producers are watching their reserves diminish.

Whats the holdup? U.S. sanctions on Iran have prevented the investment needed to develop Irans oil fields. Oil Minister Gholam Hossein Nozari said in April that, overall, $500 billion of investment would be needed in Irans oil industry during the next 15 years. Purportedly under U.S. pressure, the Japanese have been dragging their feet on an oil investment agreement that they concluded with Iran in 2004. A Malaysian company did sign a $16 billion deal with Iran last December to produce liquefied natural gas at sites including Ferdows, but it will likely be a number of years before we see crude oil flowing.

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Kashagan Field

Location: The Caspian Sea, off the coast of Kazakhstan

Estimated Reserves: 38 billion barrels

Details: Kashagan field is the largest single untapped oil field in the world and the fifth largest ever discovered. Development is underway. In fact, crude was supposed to have started flowing in 2005, but repeated delays have pushed the date to 2013. Analysts expect Kashagan to be a major source of non-OPEC oil for Europe and an important component of the continents energy security.

Whats the holdup? Setting up drilling platforms has been difficult because they must be designed to withstand the extreme weather conditions of the Caspian Sea. Moreover, the presence of pressurized natural gas and a high amount of sulfur in the oil complicate the extraction process. Ironically, the run-up in oil prices earlier this year has also increased construction costs, forcing the Kazakh government to renegotiate its production agreements and creating lengthy delays.

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West Qurna Field

Location: Southeastern Iraq

Estimated Reserves: 15-21 billion barrels

Details: The West Qurna field might hold up to 10 percent of Iraqs oil. Its already producing 100,000 barrels a day, but oil experts think further development could raise this figure to 600,000. Several international firms are bidding on West Qurna-related projects, including Russias Lukoil, the United States Chevron, and Frances Total. Lukoil has staked a claim on West Qurna, citing an agreement it signed with former President Saddam Husseins regime, but the current government has refused to recognize the claim, calling it unfair and arguing that Saddam invalidated the deal shortly before his ouster.

Whats the holdup? Two wars and more than a decade of sanctions have devastated Iraqs oil infrastructure. The threat of violence remains a huge problem. Iraqs proposed hydrocarbon law, which draws up conditions for international investment and production cooperation, would greatly speed up progress, but disagreements over how much control over production and profits should be handed to private oil companies have left the bill logjammed in parliament.

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Carioca (Sugar Loaf)

Location: The Atlantic Ocean, 275 km (171 miles) off the coast of Brazil

Estimated Reserves: 33 billion barrels

Details: Discovered late last year, the Carioca field is one of the other largest finds in the last 30 years. With only 12.2 billion barrels of proven reserves prior to the Cariocas discovery, Brazils oil industry stands to see a tremendous boost if full-scale production can be set up there. Brazilian President Luiz Incio Lula da Silva has said on several occasions that Brazil would like to join OPEC when it becomes an oil exporter. Just how much Carioca will help this cause, though, might take more than a decade to become clear.

Whats the holdup? The field is located beneath 2 km (1.2 miles) of water, several kilometers of sand and hard rock, and 2 km of salt. Until recently, technology did not exist to study oil deposits that lie beneath undersea salt formations, nor was there technology to drill at that depth. Additionally, it will be years before Brazil can even figure out just how much of its newfound treasure can be extracted.

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Chicontepec Field

Location: Mexico, north of Mexico City

Estimated Reserves: 19 billion barrels

Details: The Chicontepec field has been known since 1926. Its crude oil, however, is trapped within small compartments of fractured rock and has long been considered too challenging to extract. Only a tiny fraction of the massive reserve has been exploited. But now that production at Mexicos largest field, Cantarell, is in irreversible decline, boosting production at Chicontepec has become an urgent priority for Mexicos government.

Whats the holdup? Pemex, the Mexican oil monopoly, plans to drill more than 5,000 wells by 2012. It hopes to raise production from the current 26,000 barrels a day to 1 million barrels a day in 10 years. Due to the geological challenges, though, perhaps only 5 to 7 percent of the fields oil will ever be extracted.