Mercury Injection Porosimetry is an experimental technique, which is used to estimate capillary pressures in porous materials. The method consists of injecting mercury at increasing pressure into a sample, which has been previously evacuated; this process is known as primary drainage (the "wetting" phase is the vacuum). Recording mercury pressures and saturations allows generation of a capillary pressure-saturation curve. By next lowering the pressure in stages, an imbibition process can be simulated and the equivalent capillary pressure can be generated. A second series of pressure increases will simulate a secondary or re-drainage process; again a capillary pressure curve can be plotted. The end saturation for the primary drainage process gives an estimation of the primary drainage and the imbibition processes gives an indication of the recovery efficiency for the hydrocarbon in a reservoir (again assuming the reservoir to be water wet).

Mercury Injection Porosimetry data are used to determine pore size distributions of core samples. By using suitable scaling parameters, oil/brine capillary pressure curves may also be deducted from mercury injection capillary pressure curves. AGAT can measure mercury injection capillary pressure curves and infer pore size distribution data.