In a move that will create the second-largest offshore driller in the world, Ensco (ESV) announced its decision on Monday to buy Pride International (PDE) in a stock and cash deal valued at $7.3 billion.

Under the terms of the transaction, London-based Ensco will acquire Pride shares for $41.60 each, representing a 21% premium to Pride’s closing price on Friday.

Pride stockholders will receive 0.4778 newly-issued Ensco share plus $15.60 in cash for each share of Pride common stock. Upon consummation of the swap, Pride shareholders will own roughly 38% of Ensco.

The combined company will have 74 rigs across the globe with 21 ultra-deepwater and deepwater rigs. The offshore oil driller expects to book about $50 million in synergies in 2012 and subsequent years.

“The combination is an ideal strategic fit, as our rig types, markets, customers and expertise complement each other with minimal overlap,” said Ensco CEO Dan Rabun. “Together, we will form an even stronger company that is ideally positioned to capitalize on growth opportunities within our industry.”

Both boards of directors have unanimously approved the transaction, but the deal is still subject to shareholder approval as well as other customary closing conditions. The merger is slated to close in the second-quarter of 2011.

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