Grupo Mexico SA, the world's third-largest copper producer, purchased a Mexican railroad company from billionaire Carlos Slim, paying 3.26 billion pesos ($307 million) in stock of its transportation unit.

Slim gave Mexico City-based Grupo Mexico 100 percent of the railroad, Ferrosur SA, in exchange for a 25 percent stake in Grupo Mexico's transportation division, according to spokesmen from the two sides. Grupo Mexico already owns a Mexican railroad company, which will now operate with Ferrosur.

Grupo Mexico is seeking to strengthen its transportation division, which accounts for 18 percent of revenue, to reduce its reliance on the metal business. Ferrosur will allow Grupo Mexico to better fight competition from Kansas City Southern, owner of a 6,000-mile rail network linking the U.S. and Mexico.

"The competition with Kansas City is strong," said Juan Rebolledo, Grupo Mexico's vice president for international affairs. "Ferrosur gives us nationwide coverage."

For Slim, the transaction gives him a stake in a company that is much more competitive and valuable than Ferrosur on its own and fits his strategy to step up investment in infrastructure, said Frank Aguado, a director at Slim's bank, Grupo Financiero Inbursa SA.

Slim owned Ferrosur through Grupo Carso SA, his industrial group, and Inbursa. They had two-thirds and one-third of Ferrosur, respectively, and now will own 17 percent and 8 percent of Grupo Mexico's transportation unit, Aguado said.