This paper introduces a new, fast and robust technique that measures permeability of shale plug samples under steady-state condition. A laboratory set-up was designed and assembled which has a resolution of one millionth standard cubic centimeters per second for gas flow rate and one hundredth cubic centimeters for pore volume measurement. Extremely accurate differential transducers are used to measure the flow of gas passing through the core samples under in-situ conditions. The in-situ conditions are achieved by maintaining isothermal conditions and the application of the confining stress on the core sample. The laboratory set-up is fully automated to eliminate any human error and more importantly maintains the temperature stable within the enclosed unit. In this technique, the permeability is determined under wide range of pore and confining pressure. Klinkenberg and modified Klinkenberg methods can be then applied to evaluate the absolute permeability. When adsorbent gases such as CO2 and CH4 are used, this technique can provide the permeability hysteresis for adsorption and desorption processes. Finally, the laboratory set-up can be used to measure porosity, based on Boyle's law, formation compressibility and the sorption parameters. In this study, the laboratory set-up was used to measure permeability and porosity of Marcellus Shale core samples under wide range of pore and confining pressures using Helium as a non-adsorbent and Nitrogen and Carbon Dioxide as adsorbent gases. Both Klinkenberg and modified Klinkenberg techniques were applied to the gas permeability measurement results to obtain the absolute permeability. The permeability and porosity of the samples were found to be significantly impacted by the net stress. In contrast to porosity, the permeability exhibited hysteresis with respect to net stress.