Abstract The Mars riser systems are a major departure from those previously used on TLPs. All risers are operated with top tensions only 20% above their wet weight; the high-pressure, light-weight drilling riser has a secondary pressure barrier while drilling the majority of the well; a platform-style rig is used and all risers incorporate vortex suppression devices. These advances reduce TLP payload, reduce the risks associated with simultaneous drilling and production and minimize fatigue damage and riser interference in an area exposed to frequent Loop Current events. The design and analysis of the systems required the development and improvement of analysis tools, the performance of a multitude of hydrodynamic tests and the development of a scheme for careful tension-sharing among the three tubulars. Introduction The simplest introduction to the Mars riser systems is to compare them with the riser systems on the Auger TLP (I), which was installed in roughly the same water depth in 1993- 91. Auger was designed to use proven deepwater drilling methods and platform-like completion techniques. It uses a fixed rig, a drilling riser, a subsea BOP stack and a guidelineless reentry system very similar to those used on today's deepwater floating drilling vessels. Auger uses a surface BOP for well completions and work overs. It requires a lateral mooring system to position the rig (and thus the entire TLP) for reentries, drilling, and completions. It does not use a traditional seafloor well template and, due to the spread-well seafloor pattern, has minimal potential for riser interference. The Mars TLP utilizes a smaller, platform-style, skid able rig. The high-pressure drilling riser, in conjunction with a surface BOP, still gives a platform-style look for most drilling and completion operations. The skidable rig and gudelines eliminate the need for a lateral mooring system and allow a smaller wellbay. The system also reduces the tensioner stroke requirements by placing the surface trees nearly directly above the subsea wellheads. I t uses an Auger-style dual-casing well system and a conventional hydropneumatic tensioner system which capitalizes on the smaller stroke requirement. Development of a fuller understanding of riser-to-riser interference in storms and in Loop Current events (LCEs) has allowed the lower operating tensions and closer well spacings for Mars. Reducing VIV and manipulating riser fluids 'and coatings to control thermal effects (tension sharing variations) also help alleviate problems associatedwith low tensions. Preliminary Design Work, Concept Evaluation Dual-Casing Production Risers The Mars Production Riser System is patterned alter Auger (I). Details above and below the seabed are shown in Figure 1. Safety and operability are the predominant design goals.