The dynamics of fluids and their interaction with surfaces in Unconventional Gas Reservoirs (UGRs) are very different from those in conventional systems. The physics of flow through the matrices of these reservoirs are not well understood. The small size of flow conduits which is comparable to the gas mean free path results in a deviation from Darcy to slip, transition and free molecular flow regimes. Solving Navier-Stokes (N-S) equations with modified boundary conditions has so far been the best practical approach to describe these flow behaviours. In this paper, a study of slip flow in shale gas reservoirs is presented. Several permeability measurements were performed using three shale rock samples to study the slip permeability. The Maxwellian type slip boundary conditions were used in N-S equations to obtain the slip coefficients and tangential momentum accommodation coefficient (TMAC) in porous media from the experimental data. Our results show that slip coefficients in porous media are higher than those in non-porous systems. In addition, it is found that the TMAC is smaller in porous media in comparison to flow in non-porous materials. These observations, which are attributed to greater surface area and roughness, are in agreement with literature data, which are limited to flow through individual micro conduits. The outcomes of this study will be useful for accurate prediction of gas flow rate in shale/tight gas reservoirs when using slip boundary conditions. (C) 2016 Elsevier Ltd. All rights reserved.