A type of drillstem testing conducted with the drillstring in the hole and the surface valve closed to create a closed chamber of known volume into which the reservoir fluid can flow. The drillstring is sometimes filled with nitrogen at a relatively low pressure prior to testing. When the well begins to flow, the nitrogen or air is compressed and the volume of fluid inflow can be calculated as a function of time by monitoring the surface pressure in the drillstring. The bottomhole valve is closed to halt flow when the surface pressure reaches a value calculated prior to testing. This ensures that a precisely known amount of production has taken place.