Legislative and political timetables do not leave Mexico's Congress enough time to debate and approve a proposed oil industry overhaul by the end of this year, the country's main leftist party said Tuesday.

"There are many, many issues on the table and there is a very great deal of inflammable material," PRD chair Jesus Zambrano told a press conference.

The plan to open Mexico's state-controlled oil and gas sector to private sector participation is President Enrique Peña Nieto's most ambitious initiative since taking office last December.

Because the proposal would require changes to the constitution, it must be approved by a two-thirds majority in Congress.

Peña Nieto's package would allow private firms to invest in oil and gas exploration and production projects via profit-sharing agreements with the government.

State-owned Petroleos Mexicanos has a monopoly on the production of oil, gas and petroleum derivatives and the distribution of gasoline.

Congress already has a "super-tight" agenda, Zambrano said Tuesday.

"For time reasons, it would not be possible to enter into a general debate that demands the nation's attention," he said.

The current legislative session ends in mid-December and the energy overhaul, first put forward in August, has yet to reach the floor of either house.

Zambrano, whose party opposes the bill, urged Mexicans to keep a "cool head" when considering the issue and confirmed that the PRD is negotiating with other parties in an effort to block the initiative.

Those negotiations include lawmakers from the conservative PAN and from smaller leftist parties, PRD Sen. Miguel Barbosa said Monday.

While the left is wary of anything that could open the door to privatization of Pemex, the PAN wants to see a more extensive overhaul than that proposed by Peña Nieto's centrist Institutional Revolutionary Party, or PRI.

The PRD plans to hold a rally against the energy reform next Sunday in Mexico City.

The featured speaker will be PRD founder Cuauhtemoc Cardenas, a PRI renegade whose father, Lazaro Cardenas, nationalized the oil industry during his 1934-1940 term as president. EFE