Jorge R. Piñon, an oil expert at the University of Texas at Austin, said all the pieces were in place for the reform to deliver on its promises over the long term, although it would take time.

“The political commitment from Mexico is there,” Mr. Piñon said. “The economic and business interest from international oil companies is there. On top of that, there is a need for Mexico to increase production. There is a need for Pemex to grow as a truly independent oil company. So how can it not move forward?”

Critics on the left argue that Mexico is handing over part of its oil wealth to private companies. Past privatizations in Mexico have failed to deliver benefits to consumers, instead generating suspicions of cronyism and corruption.

In the oil industry, where Mexico is one of the top three suppliers to the United States, the government expects that foreign companies will be able to raise the output of crude. Pemex’s production has dropped to about two and a half million barrels a day, down about a million a day from its peak production a decade ago.

The government will announce in September which fields Pemex will continue to work, and then next year hold the first auction of blocs for private oil exploration and production. Investors will be watching the results closely to see how effective the overhaul will be in practice.

The technocrats at the energy ministry have modest ambitions at first, saying they expect to increase output to about three million barrels a day by 2018. Over the longer term, Mexico’s government hopes that private investment in developing oil reserves deep under the Gulf of Mexico and shale oil in northern Mexico will raise output even further.

Mexico also has rich reserves of natural gas that have not been exploited. Officials say they expect that outside investment will provide cheap gas to local companies and power plants, helping to bring down fuel costs for industry.