11 results (in terms of exceedance over GHGI values), we consider Alvarez et al. Based upon their validation with top-down studies and consistency with Brandt et al. 13 finds agreement between site-level results and top-down results, with a best estimate of supply chain emissions (including all equipment from production to distribution) ~1.8 times that of the component-level GHGI 25 (up to ~2.1× in the production-segment). A recent synthesis of site-level data by Alvarez et al. Some recent studies have used a meso-scale site-level approach which measures CH 4 down-wind of facilities (e.g., well-pads) to estimate total emissions of an entire site or facility (e.g. Top-down studies determine total emissions from multiple sites via measurements from aircraft, satellites, or weather stations (e.g. This difference is sometimes referred to as the top-down/bottom-up gap 11– 17, based on the differences in approach between the GHGI and the conflicting studies. 11 summarize the literature, and observe that national-scale estimates from large-scale field studies exceed the GHGI by ~1.5 times. However, a recurrent theme consistently found in the literature is that the GHGI underestimates total US O&NG CH 4 emissions compared to observed values 10. The GHGI uses a data-rich, bottom-up approach to estimate national CH 4 emissions by scaling up CH 4 emissions measurements from activities like well completions and gas-handling components like valves or seals. The US Environmental Protection Agency (EPA) estimates O&NG CH 4 emissions in an annual Greenhouse Gas Inventory (GHGI) 9. To this end, significant research in the past decade has investigated CH 4 emissions from the O&NG system. However, the uncertainty in this estimate, data gaps, and inconsistency with alternative approaches suggested a need for further evidence 5– 8. At the international level the contribution is approximately 5% (based on estimates from 3 and 4). According to the official United States (US) GHG inventory, CH 4 from O&NG operations are estimated to contribute ~3% of national GHG emissions (with 100 year GWP = 25, 2). During production of oil and natural gas (O&NG), some processes are designed to vent CH 4 to the air, and CH 4 is also emitted unintentionally via leaks in the system. Methane (CH 4) is the principal constituent of natural gas and is also a potent greenhouse gas (GHG) 1. If our proposed method were adopted in the United States and other jurisdictions, inventory estimates could better guide CH 4 mitigation policy priorities. We find that unintentional emissions from liquid storage tanks and other equipment leaks are the largest contributors to divergence with the GHGI. Based on an updated synthesis of measurements from component-level field studies, we develop a new inventory-based model for CH 4 emissions, for the production-segment only, that agrees within error with recent syntheses of site-level field studies and allows for isolation of equipment-level contributions. In the United States, recent synthesis studies of field measurements of CH 4 emissions at different spatial scales are ~1.5–2× greater compared to official greenhouse gas inventory (GHGI) estimates, with the production-segment as the dominant contributor to this divergence. Methane (CH 4) emissions from oil and natural gas (O&NG) systems are an important contributor to greenhouse gas emissions.