Frequently, well tests in low-permeability (tight) or low-pressure reservoirs are difficult to interpret because they do not how to the surface or sustain the now rate long enough for conventional interpretation methods to be used. An impulse-test technique has been developed to determine reservoir pressure from pressure-buildup tests. The technique is based on the wellbore-pressure solutions to an instantaneous source, including wellbore-storage (afterflow) effects. It is applicable to different flow regimes, such as cylindrically and spherically radial. It is general enough that it may be applied to a wide variety of well/test configurations, such as drillstem tests (DST＇s) and wireline formation tests in vertical and horizontal wells. It can be applied to wells in unconsolidated formations where produced sand plugs the wellbore during flow periods.