The change will not be easy for Pemex, long run as an arm of the government. For decades, the company’s task has been to pump oil and provide cash for the Mexican government, a job made possible by generous discoveries in the shallow waters of the southern gulf in the 1970s. The result was that Pemex racked up losses and never invested for the future — when the easy oil would run out. Closed off from the global industry, it fell further and further behind the energy giants.

Now, Pemex is venturing into uncharted territory, as its traditional fields decline. Since the peak in 2004, Mexican crude oil production has fallen by about a million barrels a day to an expected 2.35 million barrels a day this year.

“The tendency was for the government to look for the quick win and not have a very diversified portfolio of investment that would give you the short-term barrels, the medium-term barrels and the long-term barrels,” Mr. Lozoya said. “Obviously, the short-term barrels have been declining very quickly.”

As Mexico’s energy overhaul kicks into high gear, Pemex has neither the financial capital nor the expertise to produce oil and gas from its complex deepwater reserves. That includes the deepwater oil that the company has discovered in the Perdido Fold Belt, a deposit that extends across American and Mexican waters, or these natural gas fields further south, where the Mexican contractor Grupo R has been drilling exploratory wells with Pemex.

Similarly, Mexico has watched the shale gas boom in Texas from the sidelines. Its own deposits from the same Eagle Ford geological formation, called Agua Nueva in Spanish, are dormant because the small exploration companies working just miles across the border were excluded from Mexico by Pemex’s monopoly.

Mr. Lozoya’s priority for deep water next year is to attract partners to begin production at two fields, Trion and Maximino. He acknowledged that the companies that had developed deepwater fields on the American side of the gulf were “clear candidates.” Among those are major corporations like Exxon Mobil, Chevron and Shell.

Mr. Lozoya is also seeking partners for other types of deposits, including mature fields or extra-heavy offshore crude. That would allow Pemex to increase production quickly as it focuses on its deepwater strategy.