The reliability of measurements of relative permeabilities and capillary pressures is an important issue for reservoir engineering. Proper sampling of rocks for measurements is most important for ensuring the reliability of relative permeability and capillary pressure data. If samples are obtained improperly, costly and reliable methods for measuring rock/fluid properties may no longer be necessary or suitable. The goal of sampling should be to avoid or minimize mechanical and chemical damage to the rock. With all of these opportunities, some damage is inevitable. It should be obvious that reliable data require good measurement methods and correct treatment of the data obtained.