In this paper, outage data analysis of 66 kV and 33 kV power transformers is considered. Outage-data is obtained from the Egyptian Electricity Transmission Company. Outage-data analysis over eight years from 2002 to 2009 of 1557 transformers with MVA rating ranging from 10 MVA to 40 MVA is presented. Several indices are determined for evaluating the reliability of power transformers. The knowledge of these indices is essential for proper system planning and operation. Forced outages due to correct and false action of transformer's protection systems are carefully considered. The trend of the determined hazard function indicated that a significant number of the transformers is probably being operated in the wear-out phase; however, detailed ageing analysis is required to determine the reliability state of each transformer. The determined values for the maintainability and availability shows significant variations with time. The results are compared with the IEEE 1979 survey.