The results of a comparative probabilistic reliability model applied to offshore wind turbine systems is presented. The model calculations are based on surrogate failure rate data from industrial onshore wind turbine technologies, related marine environment technologies and generic databases. Data are adjusted for the offshore marine environment and integrated with functional as well as reliability block diagrams. The developed models are applied to five generic horizontal-axis offshore wind turbine designs. Predicted subsystem failure rates and total system failure rates are reported and critical reliability limiting sub-assemblies are identified.