The theory, design, and operation of a new probe permeameter based on a pressure-decay technique are discussed. Its useful range is from 0.001 to 30,000 md. Measurement time varies from almost-equal-to 2 to 35 seconds. Slip-corrected (KIinkenberg) and conventional gas permeabilities, both of which are free from inertial flow-resistance effects, and measurement-position coordinates are obtained automatically. Computer-stored data facilitate generation of permeability ''profiles'' (permeability/depth logs), permeability contour plots, or ''calibration'' of wireline logs that imply permeability.