The combination would create a company with gold, oil and natural gas assets around the world. Freeport said the new entity, on a pro-forma basis, would generate almost three-quarters of its 2013 operating earnings from mining and the rest from oil and gas.
The deal would help Freeport diversify, with its mining profile largely outside the United States and Plains and McMoRan concentrated in energy plays in California, Texas and the Gulf of Mexico.
Freeport said it would pay $25 cash and 0.6531 shares of its common stock for each Plains share, adding up to $50 per share, or a total deal value of $6.9bn. Freeport would pay $14.75 cash for each McMoRan share, or $2.1bn after taking into account shares in McMoRan that Freeport and Plains already own. McMoRan shareholders would also get 1.15 units of a royalty trust for each share they hold.