Molecular simulations were used to assess the potential of a new amine-functionalized metal organic framework (MOF), Zn-aminotriazolato-oxalate (Zn-Atz), in adsorption-based and membrane-based gas separations. Single-component adsorption isotherms for CO2, H-2, CH4, and N-2 were computed and compared with the available experimental isotherm data. The good agreement between experiments and simulations motivated us to predict adsorption equilibria and transport rates of CH4/H-2, CO2/H-2, CO2/CH4, and CO2/N-2 mixtures in Zn-Atz. We then used this molecular-level information to evaluate adsorption selectivity, permeation selectivity, working capacity, gas permeability, and sorbent selection parameter of Zn-Atz for CH4/H-2, CO2/H-2, CO2/CH4, and CO2/N-2 separations. The separation performance of Zn-Atz was compared with several other nanoporous adsorbents and membranes. Finally, the selectivity and permeability of mixed matrix membranes where Zn-Atz was used as filler particles were evaluated by combining molecular simulations and continuum modeling. Our results showed that this amine-functionalized MOF is a very good candidate especially for separation of CO2 from other gases both in adsorption-based and membrane-based separations due to its high affinity for CO2.