Fluid flow in hydrocarbon reservoirs and groundwater aquifers is traditionally studied by assuming that the formation permeability is constant. Such an assumption can, however, result in significant errors in the estimation of temporal and spatial variation of pressure when the formation permeability is pressure sensitive. In the present study a simple technique is proposed to obtain approximate analytical solutions to the diffusive problem with pressure-dependent formation permeability. A constant pressure test in an infinitely large system is considered. Solutions to the flow problem in linear, cylindrical, and spherical systems are derived. These solutions are then compared with the corresponding constant permeability solutions and are related to a dimensionless parameter &agr;D which is a measure of the pressure sensitivity of the formation permeability. In the present analysis the parameter &agr;D is used to define a simple relationship between the pressure-sensitive and constant permeability solutions for all three geometries. It is shown that the constant permeability solutions may underestimate the pressure distribution by approximately 10% or more for a spherical system for &agr;D=0.2. Moreover, it is demonstrated that the pressure difference between the two solutions would be most significant within a distance of a few well bore radii around the well bore and at large times. For a cylindrical system the maximum pressure difference is located at the well bore and is approximately 10% for &agr;D=0.2. ¿ American Geophysical Union 1993