Fig. 1 Schematic of this study ’ s bottom-up CH 4 emissions estimation tool. Calculation of total CH 4 emissions involves multiplication of emission factors (e.g., emissions per valve) by activity factors (e.g., number of valves per wellhead). Two sequential extrapolations are performed using an iterative bootstrapping approach. First, our database of component-level (e.g., valve, connector) emissions measurements ( a ) is extrapolated using component- level activity factors to generate equipment-level (e.g., wellhead, separator) emission factors ( b ). Second, these equipment-level emission factor distributions are extrapolated using equipment-level activity factors to generate a 2015 United States oil and natural gas production-segment CH 4 emissions estimate. This extrapolation is performed 100 times to generate a distribution of national-level CH 4 emissions ( c ) and estimate a 95% con fi dence interval (CI).