The platform is permanently moored by means of tethers or tendons grouped at each of the structure’s corners. A group of tethers is called a tension leg. As with the Seastar platform, these legs allow for significant side to side movement (up to 20 feet), with little vertical movement. Tension leg platforms can operate as deep as 7,000 feet but are best in water depths less than 5,000 ft because of their tendon design. The TLP is relatively successful at minimizing heave, pitch, and roll. However, the TLP is a relatively shallow draft structure that is expensive and limited to moderate water depths and it is virtually immobile once it has been installed. >