Subsea Well Interventions offer many challenges. The population of subsea wells is now in the region of 4000 and is anticipated to continue to grow, with expansion into deeper waters and more hostile environments. Historically, the cost of intervention on subsea wells has negatively influenced its uptake; however, this is changing with advancing technologies, as operators seek to improve recovery from their subsea assets. Fluid intervention does not require vertical well access for wireline or coiled tubing services: it involves pumping chemicals into the well in a controlled, safe manner. There are a number of fluid intervention applications, examples of which are: to protect the well against scale and hydrates; pumping of kill weight brine for the purposes of well control; cleaning the lower completion or stimulating the reservoir to tackle formation / production issues that can evolve throughout the life of the well. In 2008, an operator in the North Sea utilised the first MARS based subsea well intervention system, to carry out scale squeeze operations in the on a North Sea field from a DSV. Further successful campaigns have been completed in 2009 and 2010 in addition to a 10,000 psi system being ordered for other fields. By adopting a standardised method for scale squeeze operations, Shell has been able to reduce the cost and maximise the efficiency of their operations. Subsequently an operator in Angola has adopted the same philosophy for their subsea field while considering additional MARS options for well sampling and metering; successful operations where performed in 2009 and 2010 and 2011, allowing continuous production while reducing the cost of intervention. A major project in the Gulf of Mexico has been sanctioned where the technology will be used also. This paper will describe the operational and cost benefits of utilising MARS for subsea well intervention and update on the operational performance of this methodology as it matures.