Dec. 9 (Bloomberg) -- Petroleos Mexicanos, the state-owned oil company, will inject nitrogen into the Chicontepec field to increase output at the onshore deposit as it seeks to offset a faster-than-expected decline at its largest field.

The nitrogen injection will help the field produce 500,000 to 600,000 barrels a day of crude by 2021, the company, known as Pemex, said today in a statement e-mailed to the Mexico City stock exchange.

Pemex already injects nitrogen and other gases into offshore fields, such as Cantarell, where output has fallen for almost five years at a rate faster than the government anticipated. Nitrogen is used at Cantarell, the world’s third-largest field, to keep up pressure in the deposit, making it easier to extract the oil.

Pemex believes the Chicontepec development may hold 17.7 billion barrels of oil, the company has said. Chicontepec is primarily located in the eastern state of Veracruz.

To contact the reporter on this story: Hugh Collins in Mexico City at hcollins8@bloomberg.netAndres R. Martinez in Mexico City at amartinez28@bloomberg.net

Last Updated: December 9, 2008 16:15 EST