Oil and gas production handbook An introduction to oil and gas production

Tension Leg Platform (TLP – 
left side in picture) consists of 
a structure held in place by 
vertical tendons connected to 
the sea floor by pile-secured 
templates. The structure is 
held in a fixed position by 
tensioned tendons, which 
provide for use of the TLP in a 
broad water depth range up to 
about 2,000m. The tendons 
are constructed as hollow high 
tensile strength steel pipes that 
carry the spare buoyancy of 
the structure and ensure 
limited vertical motion. 
Semi-submersible platforms 
(front of picture) have a similar 
design but without taut 
mooring. This permits more 
lateral and vertical motion and 
is generally used with flexible 
risers and subsea wells. 
Similarly, Seastar platforms are 
miniature floating tension leg 
platforms, much like the semi-
submersible type, with 
tensioned tendons. 
SPAR consists of a single tall 
floating cylindrical hull, 
supporting a fixed deck. The 
cylinder does not, however, 
extend all the way to the 
seabed. Rather, it is tethered to 
the bottom by a series of cables and lines. The large cylinder serves to 
stabilize the platform in the water, and allows for movement to absorb the 
force of potential hurricanes. SPARs can be quite large and are used for 

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water depths from 300 up to 3,000 meters. SPAR is not an acronym, and is 
named for its resemblance to a ship's spar. SPARs can support dry 
completion wells, but are more often used with subsea wells.