The 9,515-foot well makes the third such find in the Perdido Fold Belt, located in Mexican territorial waters in the Gulf of Mexico.
Pemex says there are up to 29 billion barrels of crude equivalent in the Gulf, more than half of Mexico's potential resources.
The company has said it is interested in contracting private companies to help it tap the deepwater riches, but current legal restrictions prohibit it from engaging in joint ventures or signing production-sharing contracts.
Mexico, the world's No. 7 oil producer, has seen output drop to around 2.5 million barrels per day from a peak of 3.4 million bpd in 2004. If it cannot find and exploit new discoveries to replace declining output at its largest, aging fields, the country risks becoming a net importer of crude within a decade.
President Enrique Pena Nieto has said he will seek a sweeping energy reform aimed at boosting production by loosening restrictions on private capital in the country's oil industry. The reform proposal is expected by September.
By ROBERT KOZAK in Lima and DARCY CROWE in Bogota
Presidents of some of the most economically dynamic countries in Latin America are looking to promote a new trade group as an alternative to other regional blocs that have become more protectionist in recent years.
At a meeting this week of the Pacific Alliance, which includes Mexico, Chile, Colombia and Peru, leaders planned to work on decreasing trade barriers for goods and services, linking their stock markets and finding common ground on issues such as currency fluctuations. Their main goal is to increase trade with fast-growing Asian nations.
The leaders also will likely try to send the message that their countries are a safe place to invest in a bid to differentiate themselves from Mercosur, the South American trade bloc that includes Brazil and Argentina.
Venezuela joined Mercosur in 2012 after expropriating numerous foreign-owned firms in sectors such as food production, which relies heavily on imports. The country is now facing shortages of basic goods amid high inflation.
Mercosur frequently engages in trade squabbles and has adopted some protectionist measures in recent years. The member countries of the Pacific Alliance, meanwhile, have a strong track record of welcoming foreign investment.
"Anything that irons out the differences, that clears away overlapping rules and regulations, and makes investors more comfortable with their economic trajectory will help boost investments," said Barbara Kotschwar, a research fellow with the Peterson Institute for International Economics.
Analysts say the Pacific Alliance grew out of the failure of the earlier Free Trade Area of the Americas, which attempted to link the economies of North, Central and South America.
"It is the first time in Latin America that nations in the area have taken a leadership position on trade. It stems from a position that they took that said, 'We can do this and we need to do this,' " said Eric Farnsworth, vice president of the Council of the Americas and the Americas Society.
Enrique Peña Nieto of Mexico, Juan Manuel Santos of Colombia, Sebastián Piñera of Chile and Ollanta Humala of Peru will meet in Cali, near Colombia's Pacific coast, on Wednesday and Thursday.
Nine nations will participate as observers: Canada, Spain, Australia, New Zealand, Uruguay, Japan, Guatemala, Costa Rica and Panama.
"Its central purpose is really to enhance a common position regarding trade with Asia," said Michael Shifter, president of The Inter-American Dialogue, a Washington-based think tank.
Trade analysts say the Pacific Alliance could end up growing along the lines of the Trans-Pacific Partnership, a trade-liberalization group that started out with four countries in Asia and Latin America and now includes 12, including the U.S. and Japan. Costa Rica and Panama are candidates to join.
The alliance, which was founded in June 2012, aims to carry out an integration to allow free circulation of goods, services, capital and people. Some of the member countries have already lifted requirements for travel visas among them.
"They have been trying to avoid political rhetoric and are trying to make real advances," Mr. Shifter said.
Pacific Alliance members represent a large portion of the economy in Latin America and have posted solid economic indicators even as some of their neighbors grapple with high inflation and a significant slowdown in growth.
Data from the summit organizers shows that Mexico, Peru, Colombia and Chile account for about 35% of Latin America's combined gross domestic product. The average economic growth for the four nations was 5% in 2012 while inflation stood at 3.2%.
The four countries represent 33% of the total trade in the region and take in about a quarter of all the foreign direct investment coming into Latin America, the figures show.
"These countries share most of the same economic principles," Mr. Shifter said.
Private businesses have also taken steps toward broader integration within the member countries of the Pacific Alliance. An example is a common trading platform that has linked the bourses of Chile, Colombia and Peru. Mexico is expected to become a part of the trading system, known as MILA, in 2014.
A version of this article appeared May 22, 2013, on page A12 in the U.S. edition of The Wall Street Journal, with the headline: Latin America Seeks Asian Trade.
