At present days, the requirements on reliability analysis of power oil transformers are increasing in technical practice. Properly estimated reliability characteristics inform the user how to service machine, and such estimation also saves the user‘s financial means. In the first part of this paper, the models for estimating reliability characteristics only from a set of times to failure of power oil transformers are described. Additionally, the Cox model, which enables for such machines to complete reliability analysis with diagnostic measurements, is introduced. In the last part of this paper, the Cox model is enhanced by factor analysis and moreover, the acquired results are compared with real behaviour of tested power oil transformers during operation. and Obsahuje seznam literatury