A spar, named for logs used as buoys in shipping and moored in place vertically, is a type of floating oil platform typically used in very deep waters. Spar production platforms have been developed as an alternative to conventional platforms. 
A spar platform consists of a large-diameter, single vertical cylinder supporting a deck. The cylinder is weighted at the bottom by a chamber filled with a material that is denser than water to lower the center of gravity of the platform and provide stability. Spars are anchored to the seabed by way of a spread mooring system with either a chain-wire-chain or chain-polyester-chain composition.
There are three primary types of spars; the classic spar, truss spar, and cell spar. The classic spar consists of the cylindrical hull noted above, with the heavy ballast at the bottom of the cylinder.
A truss spar has a shorter cylindrical "hard tank" than a classic spar and has a truss structure connected to the bottom of hard tank. At the bottom of the truss structure, there is a relatively small, square shaped "soft tank" that houses the heavy ballasting material. The majority of spars are of this type.
A cell spar has a large central cylinder surrounded by smaller cylinders of alternating lengths. At the bottom of the longer cylinders is the soft tank housing the heavy ballasting material, similar to a truss spar. There is currently only one cell spar in operation.
- www.fmctechnologies.com "Glossary of Terms"
- Rigzone "How Do Spars Work?"
- Offshore Magazine "State-of-the-art of spread moored systems for deepwater floating production platforms"
- Offshore Magazine "2012 DEEPWATER SOLUTIONS & RECORDS FOR CONCEPT SELECTION"
- Exploration and Production "Red Hawk showcases first cell spar"
- www.naturalgas.org "Spar Platforms"
- Shell starts production at Perdido