A method to evaluate the probability of failure of a failure path leading to fatigue collapse of an offshore structure is presented. The failure path is modeled by a number of failure elements, which represent the fatigue-sensitive joints in the structure, connecting in parallel and failing in sequence. The probability of failure of the parallel system is calculated by using first-order second-moment method. The formulation is further improved by considering the probability of occurrence of a specified sequence in which the failure elements fail. The method can be employed both in searching for important failure paths and in evaluating the probability of failure of the whole structure in systems fatigue reliability analysis of offshore structures.