MEXICO CITY — Mexico's Senate gave final approval early on Saturday to a bill to regulate the opening of the oil and gas industries to private investment, the centerpiece of President Enrique Pena Nieto's economic reform agenda.

The Senate voted 91-26 to approve the fine print of the hydrocarbons law, which details the rules for private contracts and fines, after lawmakers gave the legislation preliminary approval early on Friday.

The bill, which fleshes out a historic overhaul of the state-run energy sector approved late last year, will now go to the lower house for likely approval before being signed into law by the president.

Following a decade of falling oil and gas output, Pena Nieto pushed through a reform in December 2013 to end state oil giant Pemex's 75-year monopoly and allow for production and exploration by private companies.

The reform is the central plank of Pena Nieto's plan to boost growth in Latin America's Number Two economy, which has lagged behind more dynamic emerging markets.

Senators are set to vote on three more energy packages, including one that opens up the electricity market to private companies which is slated to come up for debate later on Saturday.