Several empirical assumptions deriving from observations and measurements of the physical processes are involved in the modeling of Solid Oxide Fuel Cells (SOFCs). An insight of the main models proposed in the literature is given to present the characteristics and limits of these assumptions for the various existing configurations. The basic structure and equations of the models are discussed in details, focusing particularly on the parameters that are to be set to achieve reliability and accuracy. According to this discussion, a zero-dimensional model for a tubular Solid Oxide Fuel Cell (SOFC) is then presented. The model demonstrates good capability in predicting SOFC characteristic curves as they appear in the literature.