Wind power is the world’s leading source of renewable electricity, excluding hydropower, with 238,000 megawatts of capacity installed at the start of 2012. Thus far, almost all of this wind power has been tapped on land; worldwide just 4,600 megawatts of offshore wind farms were operating as of mid-2012. Offshore wind capacity is growing quickly, however, expanding nearly six-fold since 2006. Twelve countries now have wind turbines spinning offshore, and more will be joining them to take advantage of the powerful winds blowing over the oceans.