Cemex may not need to buy European Union carbon permits for its EU plants before 2020 because of an oversupply in the next two years and its expected United Nations credits.

Assuming Cemex’s UN emission-offset projects are registered, the company should be “in balance” through 2020, said Luis Farias, senior vice president of energy and climate change at the Monterrey, Mexico-based producer.

The manufacturer said it may sell additional EU allowances in 2010 if it’s successful in registering some of its 12 Clean Development Mechanism projects, effectively replacing EU permits with UN Certified Emission Reduction credits.

Carbon-reduction projects under the Clean Development Mechanism, the world’s biggest CO2-trading system after the EU program, generate Certified Emission Reduction credits, which can be used by companies for compliance in the EU market.

From three operational projects, Cemex expects 800,000 metric tons of credits a year starting in 2010 for 10 years, a total of 8 million allowances, Farias said. Cemex sold 9.1 million tons of “surplus” EU carbon dioxide allowances in the six months through December 2008 for $274 million, according to company filings. Factories across Europe may sell permits because of lower output than in 2008.