If approximately 32.5% (Los Angeles), 17.2% to 22.1% (Indianapolis), 21.5% (Washington, DC and Baltimore), and 47.1% (Boston) of total CH4 emissions are tied to slip, this constrains the quantity of fossil emissions that can be attributed to leaks and vents from distribution pipelines and other natural gas infrastructure in the cities. Using these values and the mean FFPs for each individual city, we estimate that other fossil emissions (those not associated with natural gas end-use) contribute 29.9% (Los Angeles), 35.2% to 40.1% (Indianapolis), 25.5% (Washington, DC and Baltimore), and 36.2% (Boston) to total CH4 emissions.