In this paper, investigations regarding the reliability on a typical 10MW offshore wind turbine have been carried out; in particular, different analysis methods and failure modes are considered. Moreover, the effect of propagation of each functional failure through the wind turbine is accounted. It has to be underlined that an onshore 5MW wind turbine data-base has been used; thus in order to convert the data from a 5MW onshore wind turbine into 10 MW offshore wind turbine, a proper conversion factor has been used. The reliability and availability of the whole offshore wind turbine have been calculated through the Reliability Prediction and Reliability Block Diagram (RBD). In addition, a failure mode analysis is done through FMECA, in order to pointed out the most important terms in a risk priority order. The reliability analysis has been developed using PTC Windchill Quality Solution tool.