Rock gas saturation – the degree of filling rock voids (pores, cavities, fissures) with natural gases. Gas saturation level is based in sorption capacity of minerals constituting the rock, by formation porosity and cracking factor, and by gases pressure. Quantitatively saturation is measured by gas saturation coefficient equal to the ratio between the volume of natural gas filling the voids and the volume of open pores and voids. When talking about solid commercial minerals (mainly coal) gas saturation is defined as the volume of free and retained gases (mainly methane) contained in one mass unit or volume unit of rock and extracted by way of pumping-out, vacuum-driven evacuation or liquid displacement. In natural conditions, freely escaping gases need to be taken into account for measuring gas saturation factor.

When water moves into reservoir the residual gas saturation is observed corresponding to the amount of fixed gas (trapped in pores, disengaged). Gas saturation is studied to assess the collecting properties of the reservoir, to estimate the reserves and control gas field development.