Project Final Report-08122-15-The overall project objective to develop special natural gas isotope interpretation tools for shale gas production, we have carried out an integrated theoretical and laboratory study combining synergistic efforts from both academics and industry. In particular, our theoretical studies emphasized the development of fundamental understandings of carbon and deuterium isotope fractionation changes of natural gas systems; along with the interpretation models to distinguish the sources of shale gas, i.e., primary generation vs. secondary cracking and adsorbed vs. free; as well as the theoretical interpretation model necessary to use natural gas isotope fractionation for better prediction of gas shale production decline.