A conducted Layers Of Protection Analysis of Svend oil & gas platform predicted a hazardous incident to cause up to 10 fatalities and up to 1000 MMUSD so an upgrade of the High Integrity Pressure Protection System (HIPPS) was suggested. A HIPPS is a Safety Instrumented System that must have a certain level of reliability in order to fulfill the required Safety Integrity Level (SIL) 2. The Svend HIPPS architecture and different quantitative reliability methods i.e. Reliability Block Diagrams (RBD), Fault Tree Analysis (FTA) and Markov modelling are described. Functional safety calculations i.e. the Probability of Failure on Demand (PFDAvg) are performed with each method and compared. RBD and FTA are much similar in approach but the complexity increases when using Markov modelling as the number of states may increase exponentially. However, the SIS can be described more detailed with Markov modelling. The results of the PFDAvg show a deviation within 1 % regardless of chosen method and the required SIL 2 is obtained with the proposed components and architecture for Svend topside HIPPS. It is more important that the user of a particular method is competent in using the chosen method than the method, which is actually used.