This document focuses on estimating methane emissions from the U.S. oil and natural gas supply chain using ground-based measurements at the facility level. Using these measurements, the authors estimated the magnitude of methane emissions and determined that for year 2015, supply chain emissions were approximately 60% higher than the U.S. EPA inventory estimate. The authors indicate that this difference may be due to current inventory methods and suggest that the inventory methodology could be improved and substantial methane emissions reductions can be achieved.