Floating wind energy generators have the potential to exploit wind energy resources found in much deeper waters than fixed offshore wind towers. The main difference between floating wind turbines and fixed offshore wind towers is the support system. Rather than fixed foundations on the sea floor, floating wind turbines are held in place with various anchoring systems. There are two main designs receiving large commercial investment: spar buoys and spar submersibles. Spar buoys are single-cylinder designs moored to the seabed, and are simpler and less costly to initially build, but turbine installation is harder, needing speciality ships, and they need deeper water (i.e. >100m). Spar submersibles are more complex (like small oil rigs), but can be built and assembled, and turbine installed in port and towed to their installation area. The main rationale for developing floating wind energy is that, in many ocean territories, the sea floor rapidly deepens with distance from the coastline, leaving very few locations shallower than 50m to install conventional offshore wind turbines. There are other advantages to floating wind energy that are worth mentioning. In principle, the floating turbines can be assembled on land in the controlled waters of ports and then towed offshore to their intended generation sites. Floating turbines can also be completely removed at the end of their life. The total global offshore wind energy potential is estimated as being as high as 329,600 TWh/year for capacity factors above 20% when only suitable areas for development are considered. Industry expects floating wind energy designs to become commercially competitive during the 2020s.