Accurate estimation of pore pressure is essential in almost all aspects of the oil and gas field exploration and development. Differences in pore pressure estimation could lead to drastic changes in reserve evaluation. This can especially occur in under-saturated oil reservoirs with solution gas, where gas bubbles can emerge below a certain pressure. Pore pressure is also a key factor in designing and successfully performance of hydraulic fracturing. Most overpressure determination methods rely on porosity-stress relations, where during an undrained compaction, a rock loses porosity by a rate faster than what is required to expel the pore fluid through surrounding impermeable or low permeability seal. The resultant overpressure inhibits further compaction which creates unusual signature on porosity-stress trends. However, porosity in some cases is not entirely a function of loading, which is therefore a challenge in using conventional methods of pore pressure prediction such as Eaton (1972) and Bowers (1995), even when the origin of overpressure is investigated. The main objective of this research is to undertake a contingency evaluation of the mechanisms capable of generating abnormally high pore pressure (fluid expansion, clay diagenesis, kerogen maturation, pressure transfer, etc.), and then quantify the role of each mechanism. Magnitude of overpressure is another objective of this research which will be aimed by either conducting conventional methods (in clastic rocks), or numerical modelling of the processes that contributed to overpressure generation.