Maritime piracy has been on the rise for much of the past decade, even as international efforts have helped reduce the number of successful hijackings, according to the International Maritime Bureau's (IMB) Piracy 2011 report. Large-scale attacks off the coast of Somalia in 2008 prompted the deployment of an ongoing international coalition of navies to the Gulf of Aden. A report by One Earth Future's Oceans Beyond Piracy initiative estimated Somali piracy's impact on the global economy to be $7 billion for 2011, the most detailed estimate to date. A previous report by OEF estimated the global cost of piracy for 2010 to be in the range of $7 to $12 billion.

There were 439 worldwide piracy attacks in 2011, more than half of which were attributed to Somali pirates operating in the Gulf of Aden, the Red Sea, the Arabian Sea, the Indian Ocean, and off the coast of Oman. Other piracy hotspots for 2011 included the coast off Nigeria and Benin in West Africa, and Southeast Asia, near Indonesia. In the case of Somalia, analysts say one of the largest drivers of piracy is the lack of an efficient governing authority in the country.

Pirate attacks are largely confined to four major areas: the Gulf of Aden, near Somalia and the southern entrance to the Red Sea; the Gulf of Guinea, near Nigeria and the Niger River delta; the Malacca Strait between Indonesia and Malaysia; and off the Indian subcontinent, particularly between India and Sri Lanka.

Somali pirates, by far the greatest global piracy threat, have increasingly pushed farther off the Somali coast. They have moved deeper into the Indian Ocean, off Seychelles and the Maldives, and further south along the East African coast, off Kenya, Madagascar, and Mozambique, the IMB's 2011 report says.

Somali piracy emerged as a potent force shortly after the regime of longtime Somali dictator Major General Mohamed Siad Barre collapsed in 1991. With the absence of any central governing authority, commercial fishing fleets began to exploit the country's coastline. Local fishermen responded by arming themselves, boarding illegal trawlers, and charging a fine of a few thousand dollars. "But the fishermen soon realized that the fishing fine was more lucrative than the fish," the New York Times' Jeffrey Gettleman wrote in a 2010 essay for the New York Review of Books. "By the mid-2000s," he wrote, "many part-time fishermen had graduated to full-time piracy."

Somali piracy tactics have centered on hijackings and kidnappings--lasting an average of six months--to extract large ransoms. Somali piracy has been largely free of violent tactics because it is in the pirates' interest to keep their hostages alive. In 2011, average ransom payments to Somali pirates were above $5 million, wrote Chatham House's Roger Middleton in a paper for the April 2011 Dubai School of Government conference on piracy. "The result," Middleton wrote, "is that piracy is now likely to be the second largest generator of money in Somalia, bringing in over $200 million annually."