Fault-tolerant electrohydrostatic actuator (EHA) architectures have been defined and evaluated for future military aircraft applications. The fault tolerances of these EHA architectures have been measured in terms of mission success probability and safety reliability. The functional level failure modes of an EHA and its interfacing equipment are used to analyze the required levels of redundancy and fault coverage for satisfying MIL-F-9490 probability of loss of control (PLOC), MIL-F-9490 probability of mission abort (PMA), and MIL-STD 882B fail-operational/fail-operational redundancy requirements. The study is concluded by estimating and comparing fault tolerance, performance, and weight of candidate EHA architectures. The results are summarized in a comparison matrix which may be used to select a preferred architecture for a given application. >