The deep-water field known as the Trion block will be developed by the Australian firm BHP Billiton under a "farm-out" agreement in which the leaseholder of an oil field grants an operating interest to another company to develop the field.
The Trion field is near Mexico's maritime boundary with the United States in the Gulf of Mexico and is believed to hold the equivalent of 485 million barrels of oil.
BHP Billiton said it will take a 60 percent interest in the block, while Pemex will retain 40 percent. The Australian company could eventually invest funds and give payments to Pemex totaling $624 million under the agreement.
"Today is a historic day for Pemex and Mexico, as it is the company's first association agreement," a Pemex statement said.
The National Oil Commission later said the agreement could eventually result in as much as $7.4 billion dollars.
The commission also announced the results of bidding on exploration licensing contracts for 10 other deep-water fields. Two of the contracts drew no bidders, but eight were assigned.
The commission said the eight blocks would result in a total of $34.4 billion over 35 years. It said the Mexican government would receive between 59.8 and 66.1 percent of the profits from the exploration and production projects.
Four blocks in the Perdido Fold belt, which is in the same area where Trion is located, were won mostly by foreign firms. China Offshore Oil Corporation E&P Mexico won contracts for two blocks. An alliance of Chevron, Pemex and Japan's Inpex got another block, and France's Total and ExxonMobil won the fourth.
Six deep-water blocks were offered farther south in the Salina basin. Two drew no bidders, and four were awarded, mainly to foreign firms.
An alliance of Norway's Statoil, BP and Total took two blocks. Malaysia's PC Carigali and Mexico's Sierra took another, and the U.S. Murphy Oil Corp. joined them and Britain's Ophir in winning the fourth.