There is a need to reduce air pollutant emissions in some U.S. urban regions to meet federal and state air quality guidelines. Opportunities exist for reducing pollutant emissions from natural gas appliances in the residential sector. A cost-benefit analysis on various pollutant-reducing strategies is needed to evaluate these opportunities. The effectiveness of these pollutantreducing strategies (e.g., low-emission burners, energy conservation) can then be ranked among themselves and compared with other pollutant-reducing strategies available for the region. A key step towards conducting a cost-benefit analysis is to collect information on pollutant emissions from existing residential natural gas appliances. An extensive literature search was conducted to collect data on residential natural-gas-appliance pollutant emission factors. The literature primarily describes laboratory tests and may not reflect actual emission factor distributions in the field. Pollutant emission factors for appliances operated at over 700 test conditions are summarized for nitrogen oxides, carbon monoxide, fine particulate matter, formaldehyde, and methane. The appliances for which pollutant emissions are summarized include forced-air furnaces; stand-alone space heaters (vented and unvented); water heaters; cooking range burners, ovens, and broilers; and pilot lights. The arithmetic means of the nitrogen oxides and fine particulate matter emission factor distributions agree well with the Environmental Protection Agency published emission factor values for domestic gas appliances (in report AP-42). However, the carbon monoxide and methane distribution means are much higher than the relevant AP-42 values. Formaldehyde emission factors are not addressed in AP- 42, but the emission factor mean for formaldehyde is comparable to the AP-42 emission factor value for total hydrocarbon emissions.