Well defined experiments and numerical analyses are conducted to determine the importance of dynamic effect in capillary pressure relationships for two-phase flow in porous media. Dynamic and quasi-static capillary pressure-saturation (Pc-Sw) and, ?Sw/?t-t curves are determined. These are then used to determine the dynamic effects, indicated by a dynamic coefficient (t) in the porous domains which establishes the speed at which flow equilibrium (?Sw/?t = 0) is reached. t is found to be a nonlinear function of saturation which also depends on the medium permeability. Locally determined t seems to increase as the distance of the measurement point from the fluid inlet into the domain increases. However, the functional dependence t-Sw follows similar trends at different locations within the domain. We argue that saturation weighted average of local t-Sw curves can be defined as an effective t-Sw curve for the whole domain which follows an exponential trend too. (C) 2012 American Institute of Chemical Engineers AIChE J, 2012