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The biggest draw for oil companies is Mexico’s estimated 40 billion to 60 billion barrels in untapped but technically recoverable crude reserves in the deep-water Gulf, which can be extracted at the greatest profit given today’s premium crude prices of more than $100 a barrel, Mr. Wood said.

“The ‘big money’ and the ‘big opportunity’ lies within Mexico’s deep-water plays,” he said. Global oil giants such as Exxon Mobil Corp., Chevron Corp. and Royal Dutch Shell PLC have shown interest in entering that market.

Mexico may not see as much interest in its shale oil and gas, despite having some of the world’s largest deposits, he said. Shale oil has been the province of mostly small oil companies in the U.S., such as Chesapeake Energy, which pioneered the extraction of oil from shale. The company may be reluctant to share its profits and relinquish ownership of the oil after having gone to great lengths to extract it from solid rock using expensive procedures such as hydraulic fracturing and horizontal drilling, Mr. Wood said.

Also, oil companies have shown less interest in developing vast deposits in the onshore Chicontepec field northeast of Mexico City, which contains an estimated 60 billion barrels in oil reserves but is in a geologically complex area that makes it hard to extract.

“There’s enormous amount of oil there but it’s tremendously difficult to get out of the ground,” Mr. Wood said.

With oil companies queueing up to do business in Mexico, Mr. Chandler estimates that the rise in oil production made possible by the legislation would boost Mexico’s economic growth rate by 1 to 2 percentage points a year and lead to a general upgrade of the nation’s economic outlook and credit rating.

The Wall Street credit rating agency Moody’s Investors Service last week called the planned reforms “the most significant to date for Pemex” and should brighten the outlook for Mexico and its oil company. But Moody’s said the legislation could “evolve markedly” and get diluted in the legislature, and it is waiting to see how efforts toward passage play out.

Christopher Swann, an analyst with Reuters Breakingviews, doubts that the country is ready for big changes. He said stiff opposition has forced Mr. Pena Nieto to back off his most ambitious oil reform ideas, and the limited opportunities for profits under his legislation will not attract major oil companies, which have boycotted Mexico’s efforts to spur production.

“He’s watered down plans to end the state oil monopoly to placate nationalists,” he said. “That’s bad for foreign oil companies needed to jump-start production — and shows rivals may weaken his broader agenda.”