Rig in the Gulf of Mexico owned by Mexican oil company Petróleos Mexicanos.
Area: Chicontepec Basin
Estimated barrels of recoverable crude: Over 10 billion
The U.S. gets about a third of the crude it produces from drilling in the Gulf of Mexico. U.S. offshore territory will keep producing for some time, but there are also major untapped reserves on the Mexican side of the Gulf.
They're owned by the national oil company Petróleos Mexicanos, or PEMEX. Some of the most promising plays are northeast of Mexico City and off the coast of Campeche and onshore in the Choncotepec region.
But no one besides PEMEX can really access them. Ever since Mexico kicked out foreign oil investors in 1938, the government has controlled all exploration in the country. That's been lucrative, since traditionally, the Mexican government has taken 60% of PEMEX's profits. But Mexico's oil production has slowed from near 3.4 million barrels per day in 2004 to under 2.6 million barrels per day during the beginning of 2010, squeezing those profit margins.
Mexico is starting to change the rules, but slowly. The country started offering incentives for foreign explorers and drillers to extract more oil out of its mature fields. In 2012, Mexico is expected to open up some of its newer plays to foreigners.
But while there's probably plenty of untapped oil in Mexico, the country's stringent rules about keeping all of the profits could still deter many of the majors.
See also Mexican oil may not be worth it
Last updated January 26 2011: 12:08 PM ET