In the last decades a lot of oil platforms have been built. According to Infield (Infield, 2015), there are over 800 oil platforms out in the ocean. These platforms need to be decommissioned at the end of their lifetime. The Pioneering Spirit (PS), is a state-of-the-art multi-purpose twin hull vessel with the capability to decommission and install oil and gas platforms. To lift these platforms, the vessel is equipped with the so called Topside Lift System (TLS). This system enables the vessel to decommission or install complete topsides, up to a weight of 48,000 tonnes, in one single action. During the design of the PS, limited detailed information on platforms was available. With more information revealed by various tenders, the widening procedure during the new-build-phase was initiated. However, even after this widening, the vessel is not able to handle all existing platforms. The extreme dimensions of several platforms makes it challenging to design a ship which is suitable for all platforms. In this research, the most cost effective modification to extend the topside lifting capabilities of the Pioneering Spirit is investigated. To find this modification, first the performance limiting factors, with respect to topside lifting, of the vessel are identified. Research indicates that the performance limiting factors of the vessel, are influenced by five topside characteristics. These characteristics describe the topside and its location; the weight of the topside, the length of the platform, the width of the platform, the air gap under the topside and the water-depth. The performance limiting factors are used to identify the group of platforms which cannot be lifted by the PS. This group of platforms forms the potential market for the modified vessel. For this potential market, Allseas’ platform database is used. The database is based on data of Infield (Infield, 2015) and contains over 750 platforms worldwide. For the PS, topsides with a weight of less than 10,000 tonnes are not relevant. Unfortunately, the information in the database is not complete for each platform. Platforms that lack essential information are not taken into account. The known potential market for the PS contains 37 platforms, with a topside weight range between 18,000 and 52,000 tonnes. Many of these platforms suffer from more than one limitation of the vessel. The potential platforms are used as a guideline to assess viable modification concepts. For instance, the maximum liftable weight does not need to be higher than the heaviest potential platform. There are four viable concepts generated to overcome the performance limiting factors. These are: adding additional TLS beams, extending the vessel’s bows, widening the slot and use connection bridges. These concepts are combined in several different modifications to extend the lifting capability. To be able to compare the modifications, on a ratio between the investment, running costs and income, two key figures are used. The return on investment (RoI), which indicates the efficiency of the investment (Investopedia, n.d.) and the financial result. In case the RoI of multiple modifications are equal, the financial result will be decisive. The most cost effective modification is a small modification with only the connection bridge. This modification enables the system to lift 4 additional platforms.