Methane is well-recognized as a powerful greenhouse gas (GHG), with a global warming potential (GWP) of 80.8 and 82.5 times that of CO 2 over a 20-year period. Given the short in-atmosphere lifespan of methane, combustion exhaust stream ('combustion slip'), and fugitive -unplanned releases of uncombusted gas. These categorical definitions may be ambiguous. For example, some regulatory programs categorized excess venting by malfunctions of venting components as fugitive emissions, while others consider all emissions from these components as 'vented.' Categorization plays a key role in inventory reporting. Vented and combusted sources are typically reported, although reporting methods may vary substantially in accuracy. Calculations often assume nominal, 'as planned', performance of source equipment, and fail to report failure conditions which result in excess emissions. Fugitive emissions are, by definition, unknown, and must be discovered to be reported. Reporting programs typically follow one of two methods for fugitives: (a) reporting based upon average emission factors from prior studies and counts of components or equipment units, or (b) reporting based upon multiplying a count of discovered emitters with emission factors derived from prior studies. As noted earlier, recent programmatic changes tend to encourage measurement of emissions at the component, equipment unit, or facility level to improve upon outdated emission factors.