A mathematical model of long-term solid oxide fuel cell (SOFC) degradation is proposed, based on a cross-cutting meta-study of SOFC degradation research available in the open literature. This model is able to predict long-term SOFC performance under different operating conditions, and it accounts for the main degradation mechanisms, including: Ni coarsening and oxidation; anode pore size changes; degradation of anode and electrolyte conductivity; and sulfur poisoning. The results of the study indicate that SOFCs initially degrade quickly, but that the degradation rate diminishes significantly after approximately 1200 hours of operation. Consequently, the effects of different factors associated with degradation rate are investigated, including current density, temperature, and partial pressure of H2 in fuel source. Sensitivity analyses show that current density and H2 partial pressure have the highest and the lowest impact, respectively. In addition, the model has been developed to assess sulfur poisoning within pre-reformed hydrocarbon-fuel-based SOFCs. While previous models have mostly focused on performance loss in H2-fueled SOFCs. H2S deactivates catalytic activity of the SOFCs by reducing electrochemical activity and hydrocarbon conversion. Therefore, sulfur affects SOFCs that use different fuel sources in different ways. As a result, the models developed for H2-fueled SOFCs cannot be used for hydrocarbon-fueled ones.