The common methods for determining permeability and capillarity are outlined and the uses of these results in petroleum engineering are summarized. Most of the changes noted when the single phase permeability of a specimen is determined with gas and with water are attributable to such factors as gas slippage, interactions between the media and the fluid, bacterial growth, and incomplete saturations. Multiphase permeability, used in most reservoir calculations is best determined by the unsteady state displacement method. Analyses of data obtained from well tests are based either on the assumption of steady state flow of incompressible fluids or the unsteady state flow of slightly compressible fluids. Analyses of pressure buildup curves using the concept of unsteady-state flow are proving very useful in determining a variety of reservoir conditions such as permeability, well damage, reservoir volume, distance to faults, static reset, air pressure and interference between wells. Capillary pressure relations, used to predict water saturation in the reservoir, are best determined by displacement of fluids through a semi permeable barrier. The centrifuge method gives good results in homogenous specimens, while the mercury injection method is useful for specimens not containing swelling clay minerals.