I present a model of pore pressure for argillaceous sediment that integrates the well-known undercompaction mechanism with the lesser-known chemical diagenesis mechanism. The model is based on a generalized compaction model, first-order chemical rate theory and Arrhenius rate equation, and a simple thermal-history model. The parameters of this model (activation energy, E, and the pre-exponential factor, A) are obtained from published X-ray diffraction data. I also present models for bulk density and velocity of sediment that are guided by rock-physics principles. I also discuss the relation between the current model and the Bowers model, which noted the importance of the thermal mechanisms in the context of pore-pressure prediction.