Pore principal mechanism for abnormally high pore pressure generation has been an important matter of debate for more than a decade. Among the various mechanisms proposed, mechanical overloading and aquathermal pressuring have probably received the greatest attention. Most previous discussions, however, have been based upon qualitative conceptual models. Here we propose a quantitative analysis by first examining the basic principles of porous flow and the fundamental properties of sediments and, second, by comparing the relative importance of the overloading versus the aquathermal mechanisms. The coupling between pore pressure and compaction as well as the nonlinear and path-dependent material properties are found to be critical in the present analysis. We find that although changes in stress and temperature both contribute to pressure generation, mechanical overloading is the main mechanism under normal geological conditions and is capable of producing the observed pore pressure profiles.