Abstract: A method and apparatus are provided for determining the probable location of a fault causing a power outage in a power distribution system (20) having a power distribution grid (22) and a control station (24), the power distribution grid comprising a power source (26) connected to a plurality of terminal nodes (28) by grid branches (30), and corresponding protective devices (32), whose operation minimizes the deleterious effects of power outages. More specifically, method and apparatus are provided for determining distribution system information based on the power distribution grid (22). For each report that is thereafter received of a new power outage, a set of protective devices (32) that possibly operated in response to the fault is identified by upstream tracing from the terminal node (28) to the power source (26). Using "fuzzy set" theory, the possibility that each protective device operated is calculated.