MEXICO CITY - The most dramatic overhaul of Mexico's oil industry in modern times came closer to fruition Thursday when Congress approved a proposal to end the state oil company's 75-year-old monopoly on the nation's oil and natural gas fields.

The vote marked President Enrique Pena Nieto's largest political triumph since he took office a year ago. After the 353-134 vote in the Chamber of Deputies, his supporters broke into sustained chants of "Mexico! Mexico!"

The proposal still must be approved by a majority of Mexico's 31 state legislatures and that of the federal district before it becomes enshrined in the constitution. That is expected to happen early next year; Pena Nieto's political party, the Institutional Revolutionary Party, or PRI, controls most of the state legislatures.

Once it's finally approved, the law would allow private capital, including foreign oil companies, to gain a foothold in the world's 10th-largest oil producer, something private companies have been denied since Mexico nationalized its oil industry in 1938.

In Twitter posts after the vote, Pena Nieto said it would "increase energy security of Mexico" and "boost productivity, economic growth and the generation of jobs."

Nationalization of the oil industry has been a point of pride for Mexicans for decades, and Thursday's vote brought out high emotion, particularly from nationalists who view the opening as an attack on a cornerstone of Mexican identity.

Pena Nieto made overhauling the energy industry his signature issue on taking office late last year, when he ushered the PRI back to power. It was an unprecedented position for a politician from the party, which governed Mexico during most of the 20th century and under which the oil industry was nationalized.

But Pena Nieto said allowing more participation by the private sector would inject the sagging energy sector with fresh capital and technology, and would quicken economic growth.

Should the opening of the energy sector draw significant investment and boost the economy, it might keep poorer Mexicans from seeking their fortunes in the United States.