This study focuses primarily on evaluating and reducing upstream methane emissions in the natural gas sector. This has two important implications. First, this paper in no way aims to diminish the urgent need to achieve GHG emissions reductions from other segments of the economy. For example, significant cost-effective opportunities also exist to reduce carbon dioxide emissions from both upstream and downstream stages of the natural gas life cycle, and to reduce methane emissions from coal mines, landfills, and other sources. Longer term, addressing combustion emissions will be increasingly important, whether through carbon capture and storage or by other means. Second, this paper does not address other aspects of natural gas development that pose significant risks for public health and the environment, including potential effects on drinking water and other community impacts.