Fault Tree Analysis (FTA) as a Probabilistic Risk Assessment (PRA) method is used to identify basic causes leading to an undesired event, to represent logical relation of these basic causes in leading to the event,
and finally to calculate the probability of occurrence of this event. To conduct a quantitative FTA, one needs a fault tree along with failure data of the Basic Events (BEs). Sometimes it is difficult to have an exact estimation of the failure rates of individual components or the probabilities of occurrence of undesired events due to a lack of sufficient data. Furthermore, due to imprecision in failure data of BEs, the overall result may be questionable. To avoid such conditions, a fuzzy approach may be used with the FTA technique. This reduces the ambiguity and imprecision arising from the subjectivity of data. Traditional FTA method needs a sound data base of failure of all BEs for quantifying the probability failure of system, whilst there is not such a database available in offshore pipeline industry; therefore, fuzzy FTA approach is proposed to deal with this issue. The proposed model is able to quantify the fault tree of offshore pipeline system in the absence or existence of data. This paper also illustrates with a case study the use of importance measures in sensitivity analysis.