The Senate in Mexico has approved a measure to open State-run oil fields to foreign investment.
For the first time in 75 years, private companies will be allowed explore and extract oil and gas with PEMEX and take a share of the profits.
The measure next moves to the lower house to be voted on, where it is expected to pass.
President Enrique Pena Nieto says Mexico needs to modernise its energy sector and increase oil production, which has dropped from 3.4 million barrels per day in 2004 to the current rate of 2.5 million barrels.
The Democratic Revolution Party said it is a submission to US oil companies.
The energy industry was nationalised in 1938 by President Lazaro Cardenas who asserted that Mexico had a right to its mineral wealth.