The contribution of the surface active element Phosphorus (P) in pore rounding in sintered steels is absent in popular sintering models. Instead, these mathematical models analyze the rate of mass transport, which, according to these models, is driven by chemical potential gradients set up by the differences in the curvature of the free surfaces of the compact of contacting particles. To elucidate the effect that P has on rounding of pores in sintering models, an attempt has been made to incorporate surface curvature in Gibbs’ surface thermodynamics. Using the image analysis method, a comparative study of pore morphology of sintered Iron-Carbon-Phosphorus (Fe-C-P) has been performed to study the effect P has on pore morphology. The application of the shape factor has been used to characterize the morphology of the pores. It was found that morphological enrichment and depletion of P are related to surface stresses as well as to the influence of vacancies.