May 30 (Bloomberg) -- Petroleos Mexicanos, the state-owned oil company, may add between 200,000 and 300,000 barrels of proved oil reserves for each well drilled at its onshore Chicontepec field, helping stem declining crude stocks.

Pemex plans to drill 500 wells this year at Chicontepec, which would allow the company to add as much as 150 million barrels to proved reserves, said Vinicio Suro, managing director of planning and evaluation at Pemex's exploration and production unit, during a conference in Monterrey.

``There's going to be a small jump,'' Suro said of incorporating reserves at Chicontepec. ``It's going be little by little. There's not going to be a change overnight.''

The U.S. Securities and Exchange Commission forced Pemex to remove Chicontepec from its proved reserves in 2002 because the company wasn't actively drilling in the area. Chicontepec is located mostly in the state of Veracruz.

Mexico's reserves have declined almost every year for more than two decades because Pemex has pumped more oil than it has discovered since production began in 1979 at Cantarell, the world's largest offshore oil field.

Last year, the company replaced half the proved reserves that it pumped, up from 41 percent in 2006. Pemex had oil and natural-gas reserves equivalent to 14.7 billion barrels of oil at the end of 2007.

Next year, Pemex plans to drill as many as 1,000 wells at Chicontepec, which requires sophisticated horizontal drilling techniques because it consists of the small pockets of oil and is located in densely populated rural areas.

Pemex has marked Chicontepec as one of the main areas to make up for Cantarell's declining production. Energy Minister Georgina Kessel has estimated Chicontepec may produce 600,000 barrels per day by 2021.

To contact the reporter on this story: Thomas Black in Monterrey at tblack@bloomberg.net and Andres R. Martinez in Mexico City at amartinez28@bloomberg.net

Last Updated: May 30, 2008 15:32 EDT