PepsiCo buys Rockstar Energy for $3.9 billion

PepsiCo adding more pep to its portfolio. The beverage maker is buying Rockstar Energy for $3.9 billion.

It's Pepsi's biggest push YET into the fast-growing MARKET FOR energy drinks. The company already distributes Rockstar's products in some markets.

Pepsi will add Rockstar's drinks to its own lineup, which already include Mountain Dew's Kickstart and Game Fuel brands.

Rockstar created the first energy drink offered in 16-ounce cans, and competes against the likes of Austria's Red Bull and Monster Beverage.

Arch-rival Coca-Cola owns a stake in Monster. It angered Monster when it launched its own Coke-branded energy drinks in the U.S. earlier this year. That dispute was settled after an arbitration tribunal ruled in favor of Coca-Cola.

PepsiCo shares fell in early trading Wednesday amid a broad market sell-off. Rockstar is privately held.