This paper presents an extension for linear and spherical flow conditions of the El-Khatib's method for the analysis of pressure interference tests through the use of the pressure derivative. For linear flow a graph of t / p t Ln wf ∂ ∆ ∂ vs 1/t should show a straight line with slope m l and intercept b L , which can be used to estimate the formation permeability and porosity; similarly, for spherical flow a graph of t / p t Ln wf 3 ∂ ∆ ∂ vs 1/t should show a straight line with slope m sph and intercept b sph , which can be used to estimate the same above discussed parameters. A friendly computer code for the automated analysis of pressure interference tests is also discussed. Two field cases are presented to show the use of this program. The first deals with the interference tests conducted in the naturally fractured Klamath Falls geothermal field and the second is a test carried out in a river formed bed, dominated by linear flow conditions.