Active emission periods: Reported event durations reect the entire duration of a maintenance operation, and are not necessarily indicative of the duration of emissions. Active emission periods were simulated as described in SI Section S-4. These simulations were used in all cases to estimate the practical duration of an event. In a few cases (e.g. Table -7), the probability of detecting within the duration of the event was also simulated. For production, reports connected wellheads identied by API number (a unique identication code assigned to all well bores in the U.S.) to wellpads identied by state reporting numbers (AIRS_ID). Data from CDPHE GHG reports provided metadata for 4,679 facilities (37% of facilities). These data were augmented by additional public midstream data (SI Section S-3).