Creep-fatigue data on low alloy steels were collected from National Research Institute for Metals (NRIM) Tokyo, Japan. These data were generated for lCr-Mo-V, 2.25Cr-Mo, and 9Cr-lMo steels under a wide range of test conditions. A new creep-fatigue life prediction method was developed and data compiled were assessed to examine the applicability of the new method. A brief review of the empirically based, phenomenological life prediction methods was presented where no method was found to be applicable universally to all the creep-fatigue data. The new model was developed within the viscosity concepts, in which the damage parameter was accounted for in terms of dynamic viscosity. The deformations, represented in terms of flow characteristics, generated every cycle, were proposed to culminate in the failure of the specimen when the specimen can no longer accommodate viscous flow or deformations. This method was found to be conservative under all the test conditions employed by the NRIM. In lack of assessments of the same data with other life prediction models, comments on the comparison of the analyses by various methods cannot be established.