The key properties for describing a petroleum reservoir are porosity, pore saturation, and permeability. Definitions of these terms are as follows.

Porosity refers to the capacity of the reservoir to hold fluids. It is basically the interstices, or pores, present within the reservoir rock. Typical porosities of oil reservoirs are of the order of 20%.

While porosity represents the maximum capacity of a reservoir to hold fluids, pore saturation quantifies how much of this available capacity actually does contain fluids. For example, if a reservoir is 50% saturated with oil, this means that half of the available pore space in the reservoir actually contains oil.

Permeability is a factor that quantifies how hard or how easy it is for the fluid to flow through the reservoir to the oil producing well; the greater the permeability, the easier the fluid flows.

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